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 $118.57   9.777%   $130.1626   $130.16   $130.15   $130.20  
  Purchase #2 $88.75   10.322%   $97.9108   $97.91   $97.90   $97.90  
  Purchase #3 $169.38   8.776%   $184.2448   $184.24   $184.25   $184.20  
  Purchase #4 $149.31   3.357%   $154.3223   $154.32   $154.30   $154.30  
  Purchase #5 $202.30   3.347%   $209.071   $209.07   $209.05   $209.10  
  Purchase #6 $214.47   4.816%   $224.7989   $224.80   $224.80   $224.80  
  Purchase #7 $29.86   11.334%   $33.2443   $33.24   $33.25   $33.20  
  7 purchase totals = $972.64       $1,033.7547   $1,033.74   $1,033.70   $1,033.70