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 $212.89   12.742%   $240.0164   $240.02   $240.00   $240.00  
  Purchase #2 $88.29   7.591%   $94.9921   $94.99   $95.00   $95.00  
  Purchase #3 $151.82   13.419%   $172.1927   $172.19   $172.20   $172.20  
  Purchase #4 $182.43   6.304%   $193.9304   $193.93   $193.95   $193.90  
  Purchase #5 $139.81   3.692%   $144.9718   $144.97   $144.95   $145.00  
  Purchase #6 $237.86   9.364%   $260.1332   $260.13   $260.15   $260.10  
  Purchase #7 $212.49   13.499%   $241.174   $241.17   $241.15   $241.20  
  7 purchase totals = $1,225.59       $1,347.4106   $1,347.40   $1,347.40   $1,347.40