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 $235.96   7.457%   $253.5555   $253.56   $253.55   $253.60  
  Purchase #2 $180.76   7.304%   $193.9627   $193.96   $193.95   $194.00  
  Purchase #3 $121.29   9.239%   $132.496   $132.50   $132.50   $132.50  
  Purchase #4 $167.56   10.333%   $184.874   $184.87   $184.85   $184.90  
  Purchase #5 $143.65   7.716%   $154.734   $154.73   $154.75   $154.70  
  Purchase #6 $20.85   9.367%   $22.803   $22.80   $22.80   $22.80  
  Purchase #7 $207.99   5.410%   $219.2423   $219.24   $219.25   $219.20  
  7 purchase totals = $1,078.06       $1,161.6675   $1,161.66   $1,161.65   $1,161.70