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 $193.61   9.729%   $212.4463   $212.45   $212.45   $212.40  
  Purchase #2 $180.75   13.717%   $205.5435   $205.54   $205.55   $205.50  
  Purchase #3 $197.68   9.227%   $215.9199   $215.92   $215.90   $215.90  
  Purchase #4 $115.28   7.284%   $123.677   $123.68   $123.70   $123.70  
  Purchase #5 $208.31   10.563%   $230.3138   $230.31   $230.30   $230.30  
  Purchase #6 $231.50   9.471%   $253.4254   $253.43   $253.45   $253.40  
  Purchase #7 $127.61   3.530%   $132.1146   $132.11   $132.10   $132.10  
  7 purchase totals = $1,254.74       $1,373.4405   $1,373.44   $1,373.45   $1,373.30