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 $180.86   5.818%   $191.3824   $191.38   $191.40   $191.40  
  Purchase #2 $62.31   13.466%   $70.7007   $70.70   $70.70   $70.70  
  Purchase #3 $168.57   3.104%   $173.8024   $173.80   $173.80   $173.80  
  Purchase #4 $49.92   6.625%   $53.2272   $53.23   $53.25   $53.20  
  Purchase #5 $102.94   7.565%   $110.7274   $110.73   $110.75   $110.70  
  Purchase #6 $232.47   6.125%   $246.7088   $246.71   $246.70   $246.70  
  Purchase #7 $164.44   4.443%   $171.7461   $171.75   $171.75   $171.70  
  7 purchase totals = $961.51       $1,018.2950   $1,018.30   $1,018.35   $1,018.20