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 $241.97   8.818%   $263.3069   $263.31   $263.30   $263.30  
  Purchase #2 $216.26   7.224%   $231.8826   $231.88   $231.90   $231.90  
  Purchase #3 $29.96   9.844%   $32.9093   $32.91   $32.90   $32.90  
  Purchase #4 $65.79   10.328%   $72.5848   $72.58   $72.60   $72.60  
  Purchase #5 $221.76   5.628%   $234.2407   $234.24   $234.25   $234.20  
  Purchase #6 $135.35   11.789%   $151.3064   $151.31   $151.30   $151.30  
  Purchase #7 $83.90   10.559%   $92.759   $92.76   $92.75   $92.80  
  7 purchase totals = $994.99       $1,078.9897   $1,078.99   $1,079.00   $1,079.00