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 $116.82   12.104%   $130.9599   $130.96   $130.95   $131.00  
  Purchase #2 $68.47   12.262%   $76.8658   $76.87   $76.85   $76.90  
  Purchase #3 $170.81   3.316%   $176.4741   $176.47   $176.45   $176.50  
  Purchase #4 $92.55   10.802%   $102.5473   $102.55   $102.55   $102.50  
  Purchase #5 $95.93   7.669%   $103.2869   $103.29   $103.30   $103.30  
  Purchase #6 $150.89   10.729%   $167.079   $167.08   $167.10   $167.10  
  Purchase #7 $132.44   12.270%   $148.6904   $148.69   $148.70   $148.70  
  7 purchase totals = $827.91       $905.9034   $905.91   $905.90   $906.00