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 $213.59   8.326%   $231.3735   $231.37   $231.35   $231.40  
  Purchase #2 $166.97   4.543%   $174.5554   $174.56   $174.55   $174.60  
  Purchase #3 $62.98   6.146%   $66.8508   $66.85   $66.85   $66.90  
  Purchase #4 $148.61   5.263%   $156.4313   $156.43   $156.45   $156.40  
  Purchase #5 $23.75   5.459%   $25.0465   $25.05   $25.05   $25.00  
  Purchase #6 $140.63   12.277%   $157.8951   $157.90   $157.90   $157.90  
  Purchase #7 $131.86   13.191%   $149.2537   $149.25   $149.25   $149.30  
  7 purchase totals = $888.39       $961.4063   $961.41   $961.40   $961.50