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 $12.30   12.500%   $13.8375   $13.84   $13.85   $13.80  
  Purchase #2 $207.74   6.126%   $220.4662   $220.47   $220.45   $220.50  
  Purchase #3 $216.90   9.675%   $237.8851   $237.89   $237.90   $237.90  
  Purchase #4 $182.50   9.816%   $200.4142   $200.41   $200.40   $200.40  
  Purchase #5 $26.64   9.776%   $29.2443   $29.24   $29.25   $29.20  
  Purchase #6 $110.60   8.666%   $120.1846   $120.18   $120.20   $120.20  
  Purchase #7 $60.71   12.711%   $68.4268   $68.43   $68.45   $68.40  
  7 purchase totals = $817.39       $890.4587   $890.46   $890.50   $890.40