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 $54.79   6.280%   $58.2308   $58.23   $58.25   $58.20  
  Purchase #2 $237.86   7.758%   $256.3132   $256.31   $256.30   $256.30  
  Purchase #3 $179.47   8.309%   $194.3822   $194.38   $194.40   $194.40  
  Purchase #4 $60.91   10.825%   $67.5035   $67.50   $67.50   $67.50  
  Purchase #5 $182.90   6.343%   $194.5013   $194.50   $194.50   $194.50  
  Purchase #6 $25.29   5.498%   $26.6804   $26.68   $26.70   $26.70  
  Purchase #7 $119.50   7.470%   $128.4267   $128.43   $128.45   $128.40  
  7 purchase totals = $860.72       $926.0381   $926.03   $926.10   $926.00