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 $26.58   6.314%   $28.2583   $28.26   $28.25   $28.30  
  Purchase #2 $147.94   13.311%   $167.6323   $167.63   $167.65   $167.60  
  Purchase #3 $132.82   3.325%   $137.2363   $137.24   $137.25   $137.20  
  Purchase #4 $54.48   9.306%   $59.5499   $59.55   $59.55   $59.50  
  Purchase #5 $198.34   9.727%   $217.6325   $217.63   $217.65   $217.60  
  Purchase #6 $182.61   12.507%   $205.449   $205.45   $205.45   $205.40  
  Purchase #7 $250.32   5.387%   $263.8047   $263.80   $263.80   $263.80  
  7 purchase totals = $993.09       $1,079.5630   $1,079.56   $1,079.60   $1,079.40