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 $243.35   13.523%   $276.2582   $276.26   $276.25   $276.30  
  Purchase #2 $98.30   5.364%   $103.5728   $103.57   $103.55   $103.60  
  Purchase #3 $66.55   5.518%   $70.2222   $70.22   $70.20   $70.20  
  Purchase #4 $156.68   12.424%   $176.1459   $176.15   $176.15   $176.10  
  Purchase #5 $140.45   12.773%   $158.3897   $158.39   $158.40   $158.40  
  Purchase #6 $95.85   11.350%   $106.729   $106.73   $106.75   $106.70  
  Purchase #7 $161.96   5.480%   $170.8354   $170.84   $170.85   $170.80  
  7 purchase totals = $963.14       $1,062.1532   $1,062.16   $1,062.15   $1,062.10