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 $84.59   5.103%   $88.9066   $88.91   $88.90   $88.90  
  Purchase #2 $8.48   9.409%   $9.2779   $9.28   $9.30   $9.30  
  Purchase #3 $170.75   7.182%   $183.0133   $183.01   $183.00   $183.00  
  Purchase #4 $218.52   12.546%   $245.9355   $245.94   $245.95   $245.90  
  Purchase #5 $146.56   5.530%   $154.6648   $154.66   $154.65   $154.70  
  Purchase #6 $26.60   4.563%   $27.8138   $27.81   $27.80   $27.80  
  Purchase #7 $161.61   3.191%   $166.767   $166.77   $166.75   $166.80  
  7 purchase totals = $817.11       $876.3789   $876.38   $876.35   $876.40