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 $239.84   3.373%   $247.9298   $247.93   $247.95   $247.90  
  Purchase #2 $62.51   8.447%   $67.7902   $67.79   $67.80   $67.80  
  Purchase #3 $205.88   10.141%   $226.7583   $226.76   $226.75   $226.80  
  Purchase #4 $93.65   12.295%   $105.1643   $105.16   $105.15   $105.20  
  Purchase #5 $219.97   9.612%   $241.1135   $241.11   $241.10   $241.10  
  Purchase #6 $78.66   3.291%   $81.2487   $81.25   $81.25   $81.20  
  Purchase #7 $44.25   7.701%   $47.6577   $47.66   $47.65   $47.70  
  7 purchase totals = $944.76       $1,017.6625   $1,017.66   $1,017.65   $1,017.70