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 $180.95   8.274%   $195.9218   $195.92   $195.90   $195.90  
  Purchase #2 $124.96   9.591%   $136.9449   $136.94   $136.95   $136.90  
  Purchase #3 $60.72   12.147%   $68.0957   $68.10   $68.10   $68.10  
  Purchase #4 $24.88   4.687%   $26.0461   $26.05   $26.05   $26.00  
  Purchase #5 $250.73   9.311%   $274.0755   $274.08   $274.10   $274.10  
  Purchase #6 $124.40   12.484%   $139.9301   $139.93   $139.95   $139.90  
  Purchase #7 $243.96   4.829%   $255.7408   $255.74   $255.75   $255.70  
  7 purchase totals = $1,010.60       $1,096.7549   $1,096.76   $1,096.80   $1,096.60