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 $32.87   8.642%   $35.7106   $35.71   $35.70   $35.70  
  Purchase #2 $56.93   12.212%   $63.8823   $63.88   $63.90   $63.90  
  Purchase #3 $153.70   11.692%   $171.6706   $171.67   $171.65   $171.70  
  Purchase #4 $182.75   13.731%   $207.8434   $207.84   $207.85   $207.80  
  Purchase #5 $216.68   4.114%   $225.5942   $225.59   $225.60   $225.60  
  Purchase #6 $23.95   7.451%   $25.7345   $25.73   $25.75   $25.70  
  Purchase #7 $172.85   6.485%   $184.0593   $184.06   $184.05   $184.10  
  7 purchase totals = $839.73       $914.4949   $914.48   $914.50   $914.50