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 $85.80   10.496%   $94.8056   $94.81   $94.80   $94.80  
  Purchase #2 $195.92   4.783%   $205.2909   $205.29   $205.30   $205.30  
  Purchase #3 $210.31   3.127%   $216.8864   $216.89   $216.90   $216.90  
  Purchase #4 $163.98   3.832%   $170.2637   $170.26   $170.25   $170.30  
  Purchase #5 $109.40   8.192%   $118.362   $118.36   $118.35   $118.40  
  Purchase #6 $110.38   8.582%   $119.8528   $119.85   $119.85   $119.90  
  Purchase #7 $70.50   7.365%   $75.6923   $75.69   $75.70   $75.70  
  7 purchase totals = $946.29       $1,001.1537   $1,001.15   $1,001.15   $1,001.30