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 $239.99   11.309%   $267.1305   $267.13   $267.15   $267.10  
  Purchase #2 $233.56   12.283%   $262.2482   $262.25   $262.25   $262.20  
  Purchase #3 $18.57   13.657%   $21.1061   $21.11   $21.10   $21.10  
  Purchase #4 $29.46   11.156%   $32.7466   $32.75   $32.75   $32.70  
  Purchase #5 $156.59   11.300%   $174.2847   $174.28   $174.30   $174.30  
  Purchase #6 $60.62   6.121%   $64.3306   $64.33   $64.35   $64.30  
  Purchase #7 $247.76   9.566%   $271.4607   $271.46   $271.45   $271.50  
  7 purchase totals = $986.55       $1,093.3074   $1,093.31   $1,093.35   $1,093.20