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 $42.86   12.127%   $48.0576   $48.06   $48.05   $48.10  
  Purchase #2 $101.91   7.210%   $109.2577   $109.26   $109.25   $109.30  
  Purchase #3 $57.60   12.372%   $64.7263   $64.73   $64.75   $64.70  
  Purchase #4 $244.81   13.138%   $276.9731   $276.97   $276.95   $277.00  
  Purchase #5 $181.97   13.178%   $205.95   $205.95   $205.95   $206.00  
  Purchase #6 $204.91   3.249%   $211.5675   $211.57   $211.55   $211.60  
  Purchase #7 $76.38   11.703%   $85.3188   $85.32   $85.30   $85.30  
  7 purchase totals = $910.44       $1,001.8510   $1,001.86   $1,001.80   $1,002.00