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 $194.26   3.332%   $200.7327   $200.73   $200.75   $200.70  
  Purchase #2 $66.78   3.749%   $69.2836   $69.28   $69.30   $69.30  
  Purchase #3 $119.65   13.256%   $135.5108   $135.51   $135.50   $135.50  
  Purchase #4 $88.77   11.736%   $99.188   $99.19   $99.20   $99.20  
  Purchase #5 $113.40   11.698%   $126.6655   $126.67   $126.65   $126.70  
  Purchase #6 $236.93   8.413%   $256.8629   $256.86   $256.85   $256.90  
  Purchase #7 $248.51   8.431%   $269.4619   $269.46   $269.45   $269.50  
  7 purchase totals = $1,068.30       $1,157.7054   $1,157.70   $1,157.70   $1,157.80