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 $211.72   8.261%   $229.2102   $229.21   $229.20   $229.20  
  Purchase #2 $212.37   10.793%   $235.2911   $235.29   $235.30   $235.30  
  Purchase #3 $88.97   8.513%   $96.544   $96.54   $96.55   $96.50  
  Purchase #4 $236.25   7.283%   $253.4561   $253.46   $253.45   $253.50  
  Purchase #5 $246.57   5.511%   $260.1585   $260.16   $260.15   $260.20  
  Purchase #6 $114.55   6.251%   $121.7105   $121.71   $121.70   $121.70  
  Purchase #7 $218.57   7.209%   $234.3267   $234.33   $234.35   $234.30  
  7 purchase totals = $1,329.00       $1,430.6971   $1,430.70   $1,430.70   $1,430.70