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 $53.28   12.248%   $59.8057   $59.81   $59.80   $59.80  
  Purchase #2 $104.75   10.783%   $116.0452   $116.05   $116.05   $116.00  
  Purchase #3 $149.63   12.178%   $167.8519   $167.85   $167.85   $167.90  
  Purchase #4 $225.82   3.713%   $234.2047   $234.20   $234.20   $234.20  
  Purchase #5 $126.42   3.322%   $130.6197   $130.62   $130.60   $130.60  
  Purchase #6 $45.34   13.399%   $51.4151   $51.42   $51.40   $51.40  
  Purchase #7 $249.25   3.170%   $257.1512   $257.15   $257.15   $257.20  
  7 purchase totals = $954.49       $1,017.0935   $1,017.10   $1,017.05   $1,017.10