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 $46.67   3.653%   $48.3749   $48.37   $48.35   $48.40  
  Purchase #2 $23.56   11.834%   $26.3481   $26.35   $26.35   $26.30  
  Purchase #3 $145.73   10.627%   $161.2167   $161.22   $161.20   $161.20  
  Purchase #4 $28.96   11.785%   $32.3729   $32.37   $32.35   $32.40  
  Purchase #5 $59.27   7.129%   $63.4954   $63.50   $63.50   $63.50  
  Purchase #6 $181.41   4.862%   $190.2302   $190.23   $190.25   $190.20  
  Purchase #7 $167.52   10.271%   $184.726   $184.73   $184.75   $184.70  
  7 purchase totals = $653.12       $706.7642   $706.77   $706.75   $706.70