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 $168.77   13.159%   $190.9784   $190.98   $191.00   $191.00  
  Purchase #2 $13.53   8.226%   $14.643   $14.64   $14.65   $14.60  
  Purchase #3 $123.94   3.826%   $128.6819   $128.68   $128.70   $128.70  
  Purchase #4 $221.84   8.619%   $240.9604   $240.96   $240.95   $241.00  
  Purchase #5 $207.63   8.764%   $225.8267   $225.83   $225.85   $225.80  
  Purchase #6 $24.49   11.130%   $27.2157   $27.22   $27.20   $27.20  
  Purchase #7 $171.98   11.730%   $192.1533   $192.15   $192.15   $192.20  
  7 purchase totals = $932.18       $1,020.4594   $1,020.46   $1,020.50   $1,020.50