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 $186.42   9.334%   $203.8204   $203.82   $203.80   $203.80  
  Purchase #2 $23.69   9.618%   $25.9685   $25.97   $25.95   $26.00  
  Purchase #3 $167.51   4.797%   $175.5455   $175.55   $175.55   $175.50  
  Purchase #4 $120.65   9.383%   $131.9706   $131.97   $131.95   $132.00  
  Purchase #5 $98.97   3.790%   $102.721   $102.72   $102.70   $102.70  
  Purchase #6 $209.45   13.763%   $238.2766   $238.28   $238.30   $238.30  
  Purchase #7 $89.31   8.339%   $96.7576   $96.76   $96.75   $96.80  
  7 purchase totals = $896.00       $975.0602   $975.07   $975.00   $975.10