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 $146.49   4.179%   $152.6118   $152.61   $152.60   $152.60  
  Purchase #2 $133.85   6.277%   $142.2518   $142.25   $142.25   $142.30  
  Purchase #3 $158.57   5.116%   $166.6824   $166.68   $166.70   $166.70  
  Purchase #4 $119.34   8.142%   $129.0567   $129.06   $129.05   $129.10  
  Purchase #5 $84.48   8.410%   $91.5848   $91.58   $91.60   $91.60  
  Purchase #6 $81.90   9.648%   $89.8017   $89.80   $89.80   $89.80  
  Purchase #7 $220.36   13.468%   $250.0381   $250.04   $250.05   $250.00  
  7 purchase totals = $944.99       $1,022.0273   $1,022.02   $1,022.05   $1,022.10