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 $114.82   3.263%   $118.5666   $118.57   $118.55   $118.60  
  Purchase #2 $211.78   13.584%   $240.5482   $240.55   $240.55   $240.50  
  Purchase #3 $235.67   4.686%   $246.7135   $246.71   $246.70   $246.70  
  Purchase #4 $77.80   11.806%   $86.9851   $86.99   $87.00   $87.00  
  Purchase #5 $168.38   9.643%   $184.6169   $184.62   $184.60   $184.60  
  Purchase #6 $127.32   11.415%   $141.8536   $141.85   $141.85   $141.90  
  Purchase #7 $49.57   5.104%   $52.1001   $52.10   $52.10   $52.10  
  7 purchase totals = $985.34       $1,071.3840   $1,071.39   $1,071.35   $1,071.40