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 $55.62   8.286%   $60.2287   $60.23   $60.25   $60.20  
  Purchase #2 $246.36   12.450%   $277.0318   $277.03   $277.05   $277.00  
  Purchase #3 $92.65   10.697%   $102.5608   $102.56   $102.55   $102.60  
  Purchase #4 $151.49   7.869%   $163.4107   $163.41   $163.40   $163.40  
  Purchase #5 $13.29   6.411%   $14.142   $14.14   $14.15   $14.10  
  Purchase #6 $137.30   6.487%   $146.2067   $146.21   $146.20   $146.20  
  Purchase #7 $216.51   10.259%   $238.7218   $238.72   $238.70   $238.70  
  7 purchase totals = $913.22       $1,002.3025   $1,002.30   $1,002.30   $1,002.20