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 $142.93   8.109%   $154.5202   $154.52   $154.50   $154.50  
  Purchase #2 $35.64   10.578%   $39.41   $39.41   $39.40   $39.40  
  Purchase #3 $46.58   4.604%   $48.7245   $48.72   $48.70   $48.70  
  Purchase #4 $80.84   5.788%   $85.519   $85.52   $85.50   $85.50  
  Purchase #5 $186.45   9.207%   $203.6165   $203.62   $203.60   $203.60  
  Purchase #6 $148.59   9.236%   $162.3138   $162.31   $162.30   $162.30  
  Purchase #7 $181.62   8.571%   $197.1867   $197.19   $197.20   $197.20  
  7 purchase totals = $822.65       $891.2907   $891.29   $891.20   $891.20