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 $188.86   3.297%   $195.0867   $195.09   $195.10   $195.10  
  Purchase #2 $64.56   3.476%   $66.8041   $66.80   $66.80   $66.80  
  Purchase #3 $100.81   6.388%   $107.2497   $107.25   $107.25   $107.20  
  Purchase #4 $232.69   7.260%   $249.5833   $249.58   $249.60   $249.60  
  Purchase #5 $214.85   8.841%   $233.8449   $233.84   $233.85   $233.80  
  Purchase #6 $6.89   4.626%   $7.2087   $7.21   $7.20   $7.20  
  Purchase #7 $80.65   4.182%   $84.0228   $84.02   $84.00   $84.00  
  7 purchase totals = $889.31       $943.8002   $943.79   $943.80   $943.70