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 $42.41   12.564%   $47.7384   $47.74   $47.75   $47.70  
  Purchase #2 $142.28   9.137%   $155.2801   $155.28   $155.30   $155.30  
  Purchase #3 $54.65   8.872%   $59.4985   $59.50   $59.50   $59.50  
  Purchase #4 $67.66   6.384%   $71.9794   $71.98   $72.00   $72.00  
  Purchase #5 $200.63   5.645%   $211.9556   $211.96   $211.95   $212.00  
  Purchase #6 $239.97   11.551%   $267.6889   $267.69   $267.70   $267.70  
  Purchase #7 $249.39   9.556%   $273.2217   $273.22   $273.20   $273.20  
  7 purchase totals = $996.99       $1,087.3626   $1,087.37   $1,087.40   $1,087.40