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 $32.71   12.152%   $36.6849   $36.68   $36.70   $36.70  
  Purchase #2 $195.97   9.457%   $214.5029   $214.50   $214.50   $214.50  
  Purchase #3 $53.34   5.586%   $56.3196   $56.32   $56.30   $56.30  
  Purchase #4 $205.49   13.864%   $233.9791   $233.98   $234.00   $234.00  
  Purchase #5 $48.48   8.843%   $52.7671   $52.77   $52.75   $52.80  
  Purchase #6 $152.72   6.528%   $162.6896   $162.69   $162.70   $162.70  
  Purchase #7 $219.77   3.752%   $228.0158   $228.02   $228.00   $228.00  
  7 purchase totals = $908.48       $984.9590   $984.96   $984.95   $985.00