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 $55.84   10.545%   $61.7283   $61.73   $61.75   $61.70  
  Purchase #2 $168.34   9.659%   $184.6   $184.60   $184.60   $184.60  
  Purchase #3 $237.96   12.546%   $267.8145   $267.81   $267.80   $267.80  
  Purchase #4 $66.33   11.622%   $74.0389   $74.04   $74.05   $74.00  
  Purchase #5 $187.66   13.317%   $212.6507   $212.65   $212.65   $212.70  
  Purchase #6 $115.52   8.582%   $125.4339   $125.43   $125.45   $125.40  
  Purchase #7 $72.50   4.105%   $75.4761   $75.48   $75.50   $75.50  
  7 purchase totals = $904.15       $1,001.7424   $1,001.74   $1,001.80   $1,001.70