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 $247.79   7.240%   $265.73   $265.73   $265.75   $265.70  
  Purchase #2 $150.30   13.535%   $170.6431   $170.64   $170.65   $170.60  
  Purchase #3 $65.48   3.383%   $67.6952   $67.70   $67.70   $67.70  
  Purchase #4 $179.65   9.848%   $197.3419   $197.34   $197.35   $197.30  
  Purchase #5 $184.59   7.121%   $197.7347   $197.73   $197.75   $197.70  
  Purchase #6 $36.94   12.467%   $41.5453   $41.55   $41.55   $41.50  
  Purchase #7 $112.70   5.373%   $118.7554   $118.76   $118.75   $118.80  
  7 purchase totals = $977.45       $1,059.4456   $1,059.45   $1,059.50   $1,059.30