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 $116.61   8.297%   $126.2851   $126.29   $126.30   $126.30  
  Purchase #2 $148.25   13.177%   $167.7849   $167.78   $167.80   $167.80  
  Purchase #3 $99.45   4.608%   $104.0327   $104.03   $104.05   $104.00  
  Purchase #4 $27.40   8.374%   $29.6945   $29.69   $29.70   $29.70  
  Purchase #5 $208.39   4.292%   $217.3341   $217.33   $217.35   $217.30  
  Purchase #6 $250.65   3.722%   $259.9792   $259.98   $260.00   $260.00  
  Purchase #7 $31.98   4.822%   $33.5221   $33.52   $33.50   $33.50  
  7 purchase totals = $882.73       $938.6326   $938.62   $938.70   $938.60