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 $96.57   7.839%   $104.1401   $104.14   $104.15   $104.10  
  Purchase #2 $169.78   10.345%   $187.3437   $187.34   $187.35   $187.30  
  Purchase #3 $220.71   7.601%   $237.4862   $237.49   $237.50   $237.50  
  Purchase #4 $187.95   10.452%   $207.5945   $207.59   $207.60   $207.60  
  Purchase #5 $43.52   6.427%   $46.317   $46.32   $46.30   $46.30  
  Purchase #6 $130.55   7.360%   $140.1585   $140.16   $140.15   $140.20  
  Purchase #7 $239.39   7.174%   $256.5638   $256.56   $256.55   $256.60  
  7 purchase totals = $1,088.47       $1,179.6038   $1,179.60   $1,179.60   $1,179.60