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 $203.94   11.767%   $227.9376   $227.94   $227.95   $227.90  
  Purchase #2 $68.37   5.833%   $72.358   $72.36   $72.35   $72.40  
  Purchase #3 $54.60   12.823%   $61.6014   $61.60   $61.60   $61.60  
  Purchase #4 $220.41   5.722%   $233.0219   $233.02   $233.00   $233.00  
  Purchase #5 $61.87   12.534%   $69.6248   $69.62   $69.60   $69.60  
  Purchase #6 $143.91   7.445%   $154.6241   $154.62   $154.60   $154.60  
  Purchase #7 $137.31   3.539%   $142.1694   $142.17   $142.15   $142.20  
  7 purchase totals = $890.41       $961.3372   $961.33   $961.25   $961.30