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 $49.83   10.323%   $54.974   $54.97   $54.95   $55.00  
  Purchase #2 $232.55   6.507%   $247.682   $247.68   $247.70   $247.70  
  Purchase #3 $71.59   6.157%   $75.9978   $76.00   $76.00   $76.00  
  Purchase #4 $43.27   11.443%   $48.2214   $48.22   $48.20   $48.20  
  Purchase #5 $249.66   12.411%   $280.6453   $280.65   $280.65   $280.60  
  Purchase #6 $69.96   10.773%   $77.4968   $77.50   $77.50   $77.50  
  Purchase #7 $202.34   3.712%   $209.8509   $209.85   $209.85   $209.90  
  7 purchase totals = $919.20       $994.8682   $994.87   $994.85   $994.90