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 $142.92   6.570%   $152.3098   $152.31   $152.30   $152.30  
  Purchase #2 $42.77   12.586%   $48.153   $48.15   $48.15   $48.20  
  Purchase #3 $31.60   6.513%   $33.6581   $33.66   $33.65   $33.70  
  Purchase #4 $89.84   5.138%   $94.456   $94.46   $94.45   $94.50  
  Purchase #5 $230.74   4.151%   $240.318   $240.32   $240.30   $240.30  
  Purchase #6 $194.62   8.391%   $210.9506   $210.95   $210.95   $211.00  
  Purchase #7 $99.59   8.517%   $108.0721   $108.07   $108.05   $108.10  
  7 purchase totals = $832.08       $887.9176   $887.92   $887.85   $888.10