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 $187.41   11.304%   $208.5948   $208.59   $208.60   $208.60  
  Purchase #2 $28.79   13.547%   $32.6902   $32.69   $32.70   $32.70  
  Purchase #3 $206.58   5.580%   $218.1072   $218.11   $218.10   $218.10  
  Purchase #4 $182.59   6.818%   $195.039   $195.04   $195.05   $195.00  
  Purchase #5 $159.71   11.177%   $177.5608   $177.56   $177.55   $177.60  
  Purchase #6 $203.40   3.399%   $210.3136   $210.31   $210.30   $210.30  
  Purchase #7 $112.60   10.185%   $124.0683   $124.07   $124.05   $124.10  
  7 purchase totals = $1,081.08       $1,166.3739   $1,166.37   $1,166.35   $1,166.40