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 $55.98   8.355%   $60.6571   $60.66   $60.65   $60.70  
  Purchase #2 $161.34   13.505%   $183.129   $183.13   $183.15   $183.10  
  Purchase #3 $197.29   12.191%   $221.3416   $221.34   $221.35   $221.30  
  Purchase #4 $219.27   12.758%   $247.2445   $247.24   $247.25   $247.20  
  Purchase #5 $84.86   3.818%   $88.1   $88.10   $88.10   $88.10  
  Purchase #6 $237.66   5.543%   $250.8335   $250.83   $250.85   $250.80  
  Purchase #7 $65.57   12.386%   $73.6915   $73.69   $73.70   $73.70  
  7 purchase totals = $1,021.97       $1,124.9972   $1,124.99   $1,125.05   $1,124.90