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 $247.43   8.116%   $267.5114   $267.51   $267.50   $267.50  
  Purchase #2 $31.25   7.706%   $33.6581   $33.66   $33.65   $33.70  
  Purchase #3 $160.70   6.502%   $171.1487   $171.15   $171.15   $171.10  
  Purchase #4 $124.60   3.615%   $129.1043   $129.10   $129.10   $129.10  
  Purchase #5 $159.91   3.443%   $165.4157   $165.42   $165.40   $165.40  
  Purchase #6 $208.49   13.613%   $236.8717   $236.87   $236.85   $236.90  
  Purchase #7 $8.98   4.805%   $9.4115   $9.41   $9.40   $9.40  
  7 purchase totals = $941.36       $1,013.1214   $1,013.12   $1,013.05   $1,013.10