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 $213.56   4.666%   $223.5247   $223.52   $223.50   $223.50  
  Purchase #2 $11.30   9.587%   $12.3833   $12.38   $12.40   $12.40  
  Purchase #3 $168.57   6.577%   $179.6568   $179.66   $179.65   $179.70  
  Purchase #4 $62.97   10.365%   $69.4968   $69.50   $69.50   $69.50  
  Purchase #5 $24.42   6.187%   $25.9309   $25.93   $25.95   $25.90  
  Purchase #6 $95.76   9.266%   $104.6331   $104.63   $104.65   $104.60  
  Purchase #7 $138.61   7.762%   $149.3689   $149.37   $149.35   $149.40  
  7 purchase totals = $715.19       $764.9945   $764.99   $765.00   $765.00