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 $124.94   5.759%   $132.1353   $132.14   $132.15   $132.10  
  Purchase #2 $250.91   4.336%   $261.7895   $261.79   $261.80   $261.80  
  Purchase #3 $54.58   10.787%   $60.4675   $60.47   $60.45   $60.50  
  Purchase #4 $207.35   7.157%   $222.19   $222.19   $222.20   $222.20  
  Purchase #5 $181.89   12.365%   $204.3807   $204.38   $204.40   $204.40  
  Purchase #6 $193.86   4.495%   $202.574   $202.57   $202.55   $202.60  
  Purchase #7 $215.73   7.214%   $231.2928   $231.29   $231.30   $231.30  
  7 purchase totals = $1,229.26       $1,314.8298   $1,314.83   $1,314.85   $1,314.90