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 $104.76   13.258%   $118.6491   $118.65   $118.65   $118.60  
  Purchase #2 $70.53   11.579%   $78.6967   $78.70   $78.70   $78.70  
  Purchase #3 $130.98   13.530%   $148.7016   $148.70   $148.70   $148.70  
  Purchase #4 $245.49   13.370%   $278.312   $278.31   $278.30   $278.30  
  Purchase #5 $81.90   12.338%   $92.0048   $92.00   $92.00   $92.00  
  Purchase #6 $7.70   11.342%   $8.5733   $8.57   $8.55   $8.60  
  Purchase #7 $234.78   7.367%   $252.0762   $252.08   $252.10   $252.10  
  7 purchase totals = $876.14       $977.0137   $977.01   $977.00   $977.00