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 $188.51   9.813%   $207.0085   $207.01   $207.00   $207.00  
  Purchase #2 $196.63   3.481%   $203.4747   $203.47   $203.45   $203.50  
  Purchase #3 $217.72   8.668%   $236.592   $236.59   $236.60   $236.60  
  Purchase #4 $141.48   8.818%   $153.9557   $153.96   $153.95   $154.00  
  Purchase #5 $111.71   11.225%   $124.2494   $124.25   $124.25   $124.20  
  Purchase #6 $111.40   8.383%   $120.7387   $120.74   $120.75   $120.70  
  Purchase #7 $154.70   9.148%   $168.852   $168.85   $168.85   $168.90  
  7 purchase totals = $1,122.15       $1,214.8710   $1,214.87   $1,214.85   $1,214.90