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 $173.88   13.780%   $197.8407   $197.84   $197.85   $197.80  
  Purchase #2 $246.32   12.373%   $276.7972   $276.80   $276.80   $276.80  
  Purchase #3 $85.27   3.752%   $88.4693   $88.47   $88.45   $88.50  
  Purchase #4 $180.34   8.325%   $195.3533   $195.35   $195.35   $195.40  
  Purchase #5 $196.85   3.248%   $203.2437   $203.24   $203.25   $203.20  
  Purchase #6 $126.30   3.302%   $130.4704   $130.47   $130.45   $130.50  
  Purchase #7 $14.38   8.227%   $15.563   $15.56   $15.55   $15.60  
  7 purchase totals = $1,023.34       $1,107.7376   $1,107.73   $1,107.70   $1,107.80