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 $166.68   5.170%   $175.2974   $175.30   $175.30   $175.30  
  Purchase #2 $141.43   8.613%   $153.6114   $153.61   $153.60   $153.60  
  Purchase #3 $183.99   9.852%   $202.1167   $202.12   $202.10   $202.10  
  Purchase #4 $162.99   4.109%   $169.6873   $169.69   $169.70   $169.70  
  Purchase #5 $217.39   5.112%   $228.503   $228.50   $228.50   $228.50  
  Purchase #6 $158.49   10.188%   $174.637   $174.64   $174.65   $174.60  
  Purchase #7 $209.58   10.540%   $231.6697   $231.67   $231.65   $231.70  
  7 purchase totals = $1,240.55       $1,335.5225   $1,335.53   $1,335.50   $1,335.50