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 $182.90   12.139%   $205.1022   $205.10   $205.10   $205.10  
  Purchase #2 $9.84   8.615%   $10.6877   $10.69   $10.70   $10.70  
  Purchase #3 $84.51   7.788%   $91.0916   $91.09   $91.10   $91.10  
  Purchase #4 $248.65   7.765%   $267.9577   $267.96   $267.95   $268.00  
  Purchase #5 $102.85   7.484%   $110.5473   $110.55   $110.55   $110.50  
  Purchase #6 $181.63   9.581%   $199.032   $199.03   $199.05   $199.00  
  Purchase #7 $93.70   3.727%   $97.1922   $97.19   $97.20   $97.20  
  7 purchase totals = $904.08       $981.6107   $981.61   $981.65   $981.60