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 $204.62   6.595%   $218.1147   $218.11   $218.10   $218.10  
  Purchase #2 $41.92   10.586%   $46.3577   $46.36   $46.35   $46.40  
  Purchase #3 $18.36   9.792%   $20.1578   $20.16   $20.15   $20.20  
  Purchase #4 $162.67   12.410%   $182.8573   $182.86   $182.85   $182.90  
  Purchase #5 $84.87   13.850%   $96.6245   $96.62   $96.60   $96.60  
  Purchase #6 $163.96   13.135%   $185.4961   $185.50   $185.50   $185.50  
  Purchase #7 $241.75   10.857%   $267.9968   $268.00   $268.00   $268.00  
  7 purchase totals = $918.15       $1,017.6049   $1,017.61   $1,017.55   $1,017.70