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 $223.73   8.773%   $243.3578   $243.36   $243.35   $243.40  
  Purchase #2 $74.46   12.633%   $83.8665   $83.87   $83.85   $83.90  
  Purchase #3 $66.99   7.276%   $71.8642   $71.86   $71.85   $71.90  
  Purchase #4 $149.62   8.181%   $161.8604   $161.86   $161.85   $161.90  
  Purchase #5 $83.74   3.437%   $86.6181   $86.62   $86.60   $86.60  
  Purchase #6 $195.46   9.137%   $213.3192   $213.32   $213.30   $213.30  
  Purchase #7 $50.65   10.557%   $55.9971   $56.00   $56.00   $56.00  
  7 purchase totals = $844.65       $916.8833   $916.89   $916.80   $917.00