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 $69.29   6.650%   $73.8978   $73.90   $73.90   $73.90  
  Purchase #2 $225.86   12.520%   $254.1377   $254.14   $254.15   $254.10  
  Purchase #3 $61.89   13.164%   $70.0372   $70.04   $70.05   $70.00  
  Purchase #4 $161.85   11.461%   $180.3996   $180.40   $180.40   $180.40  
  Purchase #5 $188.29   7.801%   $202.9785   $202.98   $203.00   $203.00  
  Purchase #6 $65.87   4.799%   $69.0311   $69.03   $69.05   $69.00  
  Purchase #7 $165.75   12.353%   $186.2251   $186.23   $186.25   $186.20  
  7 purchase totals = $938.80       $1,036.7070   $1,036.72   $1,036.80   $1,036.60