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 $232.94   6.231%   $247.4545   $247.45   $247.45   $247.50  
  Purchase #2 $89.31   7.168%   $95.7117   $95.71   $95.70   $95.70  
  Purchase #3 $112.78   3.176%   $116.3619   $116.36   $116.35   $116.40  
  Purchase #4 $118.64   4.667%   $124.1769   $124.18   $124.20   $124.20  
  Purchase #5 $137.40   4.288%   $143.2917   $143.29   $143.30   $143.30  
  Purchase #6 $195.51   4.343%   $204.001   $204.00   $204.00   $204.00  
  Purchase #7 $145.38   3.340%   $150.2357   $150.24   $150.25   $150.20  
  7 purchase totals = $1,031.96       $1,081.2334   $1,081.23   $1,081.25   $1,081.30