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 $60.83   12.628%   $68.5116   $68.51   $68.50   $68.50  
  Purchase #2 $223.37   13.638%   $253.8332   $253.83   $253.85   $253.80  
  Purchase #3 $145.56   3.543%   $150.7172   $150.72   $150.70   $150.70  
  Purchase #4 $94.60   12.755%   $106.6662   $106.67   $106.65   $106.70  
  Purchase #5 $234.91   11.320%   $261.5018   $261.50   $261.50   $261.50  
  Purchase #6 $104.65   3.411%   $108.2196   $108.22   $108.20   $108.20  
  Purchase #7 $242.54   7.697%   $261.2083   $261.21   $261.20   $261.20  
  7 purchase totals = $1,106.46       $1,210.6579   $1,210.66   $1,210.60   $1,210.60