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 $68.93   3.714%   $71.4901   $71.49   $71.50   $71.50  
  Purchase #2 $213.47   9.567%   $233.8927   $233.89   $233.90   $233.90  
  Purchase #3 $223.49   13.654%   $254.0053   $254.01   $254.00   $254.00  
  Purchase #4 $97.45   5.646%   $102.952   $102.95   $102.95   $103.00  
  Purchase #5 $148.31   9.862%   $162.9363   $162.94   $162.95   $162.90  
  Purchase #6 $160.97   3.517%   $166.6313   $166.63   $166.65   $166.60  
  Purchase #7 $118.76   13.861%   $135.2213   $135.22   $135.20   $135.20  
  7 purchase totals = $1,031.38       $1,127.1290   $1,127.13   $1,127.15   $1,127.10