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 $168.27   13.679%   $191.2877   $191.29   $191.30   $191.30  
  Purchase #2 $231.91   12.827%   $261.6571   $261.66   $261.65   $261.70  
  Purchase #3 $141.45   8.637%   $153.667   $153.67   $153.65   $153.70  
  Purchase #4 $71.66   5.185%   $75.3756   $75.38   $75.40   $75.40  
  Purchase #5 $158.72   8.578%   $172.335   $172.34   $172.35   $172.30  
  Purchase #6 $143.66   4.646%   $150.3344   $150.33   $150.35   $150.30  
  Purchase #7 $218.30   6.365%   $232.1948   $232.19   $232.20   $232.20  
  7 purchase totals = $1,133.97       $1,236.8516   $1,236.86   $1,236.90   $1,236.90