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 $86.46   8.135%   $93.4935   $93.49   $93.50   $93.50  
  Purchase #2 $232.82   5.124%   $244.7497   $244.75   $244.75   $244.70  
  Purchase #3 $159.95   5.590%   $168.8912   $168.89   $168.90   $168.90  
  Purchase #4 $160.73   9.775%   $176.4414   $176.44   $176.45   $176.40  
  Purchase #5 $200.71   11.267%   $223.324   $223.32   $223.30   $223.30  
  Purchase #6 $240.64   6.465%   $256.1974   $256.20   $256.20   $256.20  
  Purchase #7 $34.28   4.490%   $35.8192   $35.82   $35.80   $35.80  
  7 purchase totals = $1,115.59       $1,198.9164   $1,198.91   $1,198.90   $1,198.80