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 $245.94   8.296%   $266.3432   $266.34   $266.35   $266.30  
  Purchase #2 $204.82   6.136%   $217.3878   $217.39   $217.40   $217.40  
  Purchase #3 $237.56   6.419%   $252.809   $252.81   $252.80   $252.80  
  Purchase #4 $187.41   13.187%   $212.1238   $212.12   $212.10   $212.10  
  Purchase #5 $144.84   6.277%   $153.9316   $153.93   $153.95   $153.90  
  Purchase #6 $217.36   9.389%   $237.7679   $237.77   $237.75   $237.80  
  Purchase #7 $16.64   13.775%   $18.9322   $18.93   $18.95   $18.90  
  7 purchase totals = $1,254.57       $1,359.2955   $1,359.29   $1,359.30   $1,359.20