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 $248.91   11.415%   $277.3231   $277.32   $277.30   $277.30  
  Purchase #2 $25.28   3.842%   $26.2513   $26.25   $26.25   $26.30  
  Purchase #3 $226.71   9.196%   $247.5583   $247.56   $247.55   $247.60  
  Purchase #4 $88.62   7.764%   $95.5005   $95.50   $95.50   $95.50  
  Purchase #5 $151.74   10.102%   $167.0688   $167.07   $167.05   $167.10  
  Purchase #6 $184.90   13.581%   $210.0113   $210.01   $210.00   $210.00  
  Purchase #7 $191.98   13.494%   $217.8858   $217.89   $217.90   $217.90  
  7 purchase totals = $1,118.14       $1,241.5991   $1,241.60   $1,241.55   $1,241.70