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 $140.34   10.667%   $155.3101   $155.31   $155.30   $155.30  
  Purchase #2 $61.53   11.418%   $68.5555   $68.56   $68.55   $68.60  
  Purchase #3 $234.88   5.124%   $246.9153   $246.92   $246.90   $246.90  
  Purchase #4 $162.95   5.801%   $172.4027   $172.40   $172.40   $172.40  
  Purchase #5 $133.29   6.334%   $141.7326   $141.73   $141.75   $141.70  
  Purchase #6 $205.58   4.435%   $214.6975   $214.70   $214.70   $214.70  
  Purchase #7 $239.38   10.819%   $265.2785   $265.28   $265.30   $265.30  
  7 purchase totals = $1,177.95       $1,264.8922   $1,264.90   $1,264.90   $1,264.90