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 $166.25   4.168%   $173.1793   $173.18   $173.20   $173.20  
  Purchase #2 $232.65   13.844%   $264.8581   $264.86   $264.85   $264.90  
  Purchase #3 $177.93   6.181%   $188.9279   $188.93   $188.95   $188.90  
  Purchase #4 $176.28   11.797%   $197.0758   $197.08   $197.10   $197.10  
  Purchase #5 $206.47   4.578%   $215.9222   $215.92   $215.90   $215.90  
  Purchase #6 $91.58   13.580%   $104.0166   $104.02   $104.00   $104.00  
  Purchase #7 $97.33   12.427%   $109.4252   $109.43   $109.45   $109.40  
  7 purchase totals = $1,148.49       $1,253.4051   $1,253.42   $1,253.45   $1,253.40