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 $225.83   9.179%   $246.5589   $246.56   $246.55   $246.60  
  Purchase #2 $132.25   11.494%   $147.4508   $147.45   $147.45   $147.50  
  Purchase #3 $188.78   11.208%   $209.9385   $209.94   $209.95   $209.90  
  Purchase #4 $161.95   9.698%   $177.6559   $177.66   $177.65   $177.70  
  Purchase #5 $56.80   9.654%   $62.2835   $62.28   $62.30   $62.30  
  Purchase #6 $67.64   13.331%   $76.6571   $76.66   $76.65   $76.70  
  Purchase #7 $151.43   10.416%   $167.2029   $167.20   $167.20   $167.20  
  7 purchase totals = $984.68       $1,087.7476   $1,087.75   $1,087.75   $1,087.90