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 $91.87   5.871%   $97.2637   $97.26   $97.25   $97.30  
  Purchase #2 $240.42   13.500%   $272.8767   $272.88   $272.90   $272.90  
  Purchase #3 $158.87   5.309%   $167.3044   $167.30   $167.30   $167.30  
  Purchase #4 $91.99   3.143%   $94.8812   $94.88   $94.90   $94.90  
  Purchase #5 $149.66   7.260%   $160.5253   $160.53   $160.55   $160.50  
  Purchase #6 $155.86   6.118%   $165.3955   $165.40   $165.40   $165.40  
  Purchase #7 $109.53   6.443%   $116.587   $116.59   $116.60   $116.60  
  7 purchase totals = $998.20       $1,074.8338   $1,074.84   $1,074.90   $1,074.90