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 $248.72   7.447%   $267.2422   $267.24   $267.25   $267.20  
  Purchase #2 $93.69   9.197%   $102.3067   $102.31   $102.30   $102.30  
  Purchase #3 $229.69   5.631%   $242.6238   $242.62   $242.60   $242.60  
  Purchase #4 $204.53   7.306%   $219.473   $219.47   $219.45   $219.50  
  Purchase #5 $126.35   6.620%   $134.7144   $134.71   $134.70   $134.70  
  Purchase #6 $246.56   4.273%   $257.0955   $257.10   $257.10   $257.10  
  Purchase #7 $80.83   6.324%   $85.9417   $85.94   $85.95   $85.90  
  7 purchase totals = $1,230.37       $1,309.3973   $1,309.39   $1,309.35   $1,309.30