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 $52.94   10.682%   $58.5951   $58.60   $58.60   $58.60  
  Purchase #2 $58.25   13.118%   $65.8912   $65.89   $65.90   $65.90  
  Purchase #3 $206.85   8.761%   $224.9721   $224.97   $224.95   $225.00  
  Purchase #4 $119.39   10.276%   $131.6585   $131.66   $131.65   $131.70  
  Purchase #5 $52.96   6.140%   $56.2117   $56.21   $56.20   $56.20  
  Purchase #6 $178.69   11.112%   $198.546   $198.55   $198.55   $198.50  
  Purchase #7 $115.56   8.207%   $125.044   $125.04   $125.05   $125.00  
  7 purchase totals = $784.64       $860.9186   $860.92   $860.90   $860.90