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 $250.54   5.771%   $264.9987   $265.00   $265.00   $265.00  
  Purchase #2 $150.71   12.694%   $169.8411   $169.84   $169.85   $169.80  
  Purchase #3 $6.95   6.334%   $7.3902   $7.39   $7.40   $7.40  
  Purchase #4 $18.73   5.292%   $19.7212   $19.72   $19.70   $19.70  
  Purchase #5 $83.62   9.794%   $91.8097   $91.81   $91.80   $91.80  
  Purchase #6 $225.65   3.468%   $233.4755   $233.48   $233.50   $233.50  
  Purchase #7 $204.93   7.683%   $220.6748   $220.67   $220.65   $220.70  
  7 purchase totals = $941.13       $1,007.9112   $1,007.91   $1,007.90   $1,007.90