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 $54.34   7.719%   $58.5345   $58.53   $58.55   $58.50  
  Purchase #2 $189.66   4.353%   $197.9159   $197.92   $197.90   $197.90  
  Purchase #3 $209.49   6.232%   $222.5454   $222.55   $222.55   $222.50  
  Purchase #4 $171.73   11.490%   $191.4618   $191.46   $191.45   $191.50  
  Purchase #5 $38.91   5.475%   $41.0403   $41.04   $41.05   $41.00  
  Purchase #6 $155.66   7.195%   $166.8597   $166.86   $166.85   $166.90  
  Purchase #7 $34.45   12.387%   $38.7173   $38.72   $38.70   $38.70  
  7 purchase totals = $854.24       $917.0749   $917.08   $917.05   $917.00