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 $248.27   13.868%   $282.7001   $282.70   $282.70   $282.70  
  Purchase #2 $227.40   3.636%   $235.6683   $235.67   $235.65   $235.70  
  Purchase #3 $32.31   7.226%   $34.6447   $34.64   $34.65   $34.60  
  Purchase #4 $9.43   11.445%   $10.5093   $10.51   $10.50   $10.50  
  Purchase #5 $174.40   9.667%   $191.2592   $191.26   $191.25   $191.30  
  Purchase #6 $125.74   4.688%   $131.6347   $131.63   $131.65   $131.60  
  Purchase #7 $171.84   4.750%   $180.0024   $180.00   $180.00   $180.00  
  7 purchase totals = $989.39       $1,066.4187   $1,066.41   $1,066.40   $1,066.40