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 $183.33   12.534%   $206.3086   $206.31   $206.30   $206.30  
  Purchase #2 $234.88   11.545%   $261.9969   $262.00   $262.00   $262.00  
  Purchase #3 $235.92   5.672%   $249.3014   $249.30   $249.30   $249.30  
  Purchase #4 $156.75   9.135%   $171.0691   $171.07   $171.05   $171.10  
  Purchase #5 $12.76   11.663%   $14.2482   $14.25   $14.25   $14.20  
  Purchase #6 $163.43   11.295%   $181.8894   $181.89   $181.90   $181.90  
  Purchase #7 $22.92   12.787%   $25.8508   $25.85   $25.85   $25.90  
  7 purchase totals = $1,009.99       $1,110.6644   $1,110.67   $1,110.65   $1,110.70