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 $92.41   4.739%   $96.7893   $96.79   $96.80   $96.80  
  Purchase #2 $244.94   6.374%   $260.5525   $260.55   $260.55   $260.60  
  Purchase #3 $103.61   11.372%   $115.3925   $115.39   $115.40   $115.40  
  Purchase #4 $226.96   7.179%   $243.2535   $243.25   $243.25   $243.30  
  Purchase #5 $186.63   7.666%   $200.9371   $200.94   $200.95   $200.90  
  Purchase #6 $150.37   12.347%   $168.9362   $168.94   $168.95   $168.90  
  Purchase #7 $103.75   9.782%   $113.8988   $113.90   $113.90   $113.90  
  7 purchase totals = $1,108.67       $1,199.7599   $1,199.76   $1,199.80   $1,199.80