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 $55.46   11.506%   $61.8412   $61.84   $61.85   $61.80  
  Purchase #2 $242.94   10.459%   $268.3491   $268.35   $268.35   $268.30  
  Purchase #3 $118.37   3.219%   $122.1803   $122.18   $122.20   $122.20  
  Purchase #4 $180.29   5.752%   $190.6603   $190.66   $190.65   $190.70  
  Purchase #5 $58.73   4.675%   $61.4756   $61.48   $61.50   $61.50  
  Purchase #6 $202.92   7.201%   $217.5323   $217.53   $217.55   $217.50  
  Purchase #7 $100.48   8.786%   $109.3082   $109.31   $109.30   $109.30  
  7 purchase totals = $959.19       $1,031.3470   $1,031.35   $1,031.40   $1,031.30