Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $190.75   6.384%   $202.9275   $202.93   $202.95   $202.90  
  Purchase #2 $113.86   8.221%   $123.2204   $123.22   $123.20   $123.20  
  Purchase #3 $159.29   13.177%   $180.2796   $180.28   $180.30   $180.30  
  Purchase #4 $192.85   4.398%   $201.3315   $201.33   $201.35   $201.30  
  Purchase #5 $229.47   12.666%   $258.5347   $258.53   $258.55   $258.50  
  Purchase #6 $238.29   3.762%   $247.2545   $247.25   $247.25   $247.30  
  Purchase #7 $150.68   6.127%   $159.9122   $159.91   $159.90   $159.90  
  7 purchase totals = $1,275.19       $1,373.4604   $1,373.45   $1,373.50   $1,373.40