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 $204.85   5.209%   $215.5206   $215.52   $215.50   $215.50  
  Purchase #2 $96.88   5.618%   $102.3227   $102.32   $102.30   $102.30  
  Purchase #3 $44.38   9.463%   $48.5797   $48.58   $48.60   $48.60  
  Purchase #4 $210.64   10.714%   $233.208   $233.21   $233.20   $233.20  
  Purchase #5 $177.27   3.361%   $183.228   $183.23   $183.25   $183.20  
  Purchase #6 $17.56   6.360%   $18.6768   $18.68   $18.70   $18.70  
  Purchase #7 $18.67   3.712%   $19.363   $19.36   $19.35   $19.40  
  7 purchase totals = $770.25       $820.8988   $820.90   $820.90   $820.90