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 $94.87   13.706%   $107.8729   $107.87   $107.85   $107.90  
  Purchase #2 $188.87   4.219%   $196.8384   $196.84   $196.85   $196.80  
  Purchase #3 $148.90   13.776%   $169.4125   $169.41   $169.40   $169.40  
  Purchase #4 $230.56   12.801%   $260.074   $260.07   $260.05   $260.10  
  Purchase #5 $181.78   11.819%   $203.2646   $203.26   $203.25   $203.30  
  Purchase #6 $246.96   8.773%   $268.6258   $268.63   $268.65   $268.60  
  Purchase #7 $169.90   9.390%   $185.8536   $185.85   $185.85   $185.90  
  7 purchase totals = $1,261.84       $1,391.9418   $1,391.93   $1,391.90   $1,392.00