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 $67.58   7.711%   $72.7911   $72.79   $72.80   $72.80  
  Purchase #2 $182.67   10.390%   $201.6494   $201.65   $201.65   $201.60  
  Purchase #3 $23.61   6.327%   $25.1038   $25.10   $25.10   $25.10  
  Purchase #4 $6.81   10.206%   $7.505   $7.51   $7.50   $7.50  
  Purchase #5 $132.94   6.504%   $141.5864   $141.59   $141.60   $141.60  
  Purchase #6 $64.87   9.281%   $70.8906   $70.89   $70.90   $70.90  
  Purchase #7 $81.84   3.133%   $84.404   $84.40   $84.40   $84.40  
  7 purchase totals = $560.32       $603.9303   $603.93   $603.95   $603.90