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 $197.52   6.600%   $210.5563   $210.56   $210.55   $210.60  
  Purchase #2 $201.29   5.716%   $212.7957   $212.80   $212.80   $212.80  
  Purchase #3 $60.98   3.237%   $62.9539   $62.95   $62.95   $63.00  
  Purchase #4 $195.45   11.524%   $217.9737   $217.97   $217.95   $218.00  
  Purchase #5 $118.71   3.640%   $123.031   $123.03   $123.05   $123.00  
  Purchase #6 $172.49   9.689%   $189.2026   $189.20   $189.20   $189.20  
  Purchase #7 $126.47   6.746%   $135.0017   $135.00   $135.00   $135.00  
  7 purchase totals = $1,072.91       $1,151.5149   $1,151.51   $1,151.50   $1,151.60