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 $53.87   9.369%   $58.9171   $58.92   $58.90   $58.90  
  Purchase #2 $151.50   5.423%   $159.7158   $159.72   $159.70   $159.70  
  Purchase #3 $160.95   6.611%   $171.5904   $171.59   $171.60   $171.60  
  Purchase #4 $165.27   8.867%   $179.9245   $179.92   $179.90   $179.90  
  Purchase #5 $213.27   9.774%   $234.115   $234.12   $234.10   $234.10  
  Purchase #6 $91.26   6.183%   $96.9026   $96.90   $96.90   $96.90  
  Purchase #7 $52.27   3.603%   $54.1533   $54.15   $54.15   $54.20  
  7 purchase totals = $888.39       $955.3187   $955.32   $955.25   $955.30