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 $54.46   8.644%   $59.1675   $59.17   $59.15   $59.20  
  Purchase #2 $69.85   6.587%   $74.451   $74.45   $74.45   $74.50  
  Purchase #3 $206.65   10.589%   $228.5322   $228.53   $228.55   $228.50  
  Purchase #4 $95.86   9.312%   $104.7865   $104.79   $104.80   $104.80  
  Purchase #5 $108.97   5.443%   $114.9012   $114.90   $114.90   $114.90  
  Purchase #6 $32.42   4.807%   $33.9784   $33.98   $34.00   $34.00  
  Purchase #7 $88.28   12.230%   $99.0766   $99.08   $99.10   $99.10  
  7 purchase totals = $656.49       $714.8934   $714.90   $714.95   $715.00