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 $139.52   6.362%   $148.3963   $148.40   $148.40   $148.40  
  Purchase #2 $245.76   13.812%   $279.7044   $279.70   $279.70   $279.70  
  Purchase #3 $124.59   11.609%   $139.0537   $139.05   $139.05   $139.10  
  Purchase #4 $202.72   4.738%   $212.3249   $212.32   $212.30   $212.30  
  Purchase #5 $23.94   3.343%   $24.7403   $24.74   $24.75   $24.70  
  Purchase #6 $112.73   3.336%   $116.4907   $116.49   $116.50   $116.50  
  Purchase #7 $106.43   8.802%   $115.798   $115.80   $115.80   $115.80  
  7 purchase totals = $955.69       $1,036.5083   $1,036.50   $1,036.50   $1,036.50