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 $24.44   13.110%   $27.6441   $27.64   $27.65   $27.60  
  Purchase #2 $235.75   6.363%   $250.7508   $250.75   $250.75   $250.80  
  Purchase #3 $127.87   4.440%   $133.5474   $133.55   $133.55   $133.50  
  Purchase #4 $23.88   5.260%   $25.1361   $25.14   $25.15   $25.10  
  Purchase #5 $250.31   3.721%   $259.624   $259.62   $259.60   $259.60  
  Purchase #6 $159.93   6.612%   $170.5046   $170.50   $170.50   $170.50  
  Purchase #7 $199.53   13.307%   $226.0815   $226.08   $226.10   $226.10  
  7 purchase totals = $1,021.71       $1,093.2885   $1,093.28   $1,093.30   $1,093.20