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 $189.76   3.792%   $196.9557   $196.96   $196.95   $197.00  
  Purchase #2 $45.96   7.218%   $49.2774   $49.28   $49.30   $49.30  
  Purchase #3 $181.49   3.187%   $187.2741   $187.27   $187.25   $187.30  
  Purchase #4 $162.63   9.272%   $177.7091   $177.71   $177.70   $177.70  
  Purchase #5 $42.72   8.788%   $46.4742   $46.47   $46.45   $46.50  
  Purchase #6 $202.39   6.238%   $215.0151   $215.02   $215.00   $215.00  
  Purchase #7 $235.64   8.205%   $254.9743   $254.97   $254.95   $255.00  
  7 purchase totals = $1,060.59       $1,127.6799   $1,127.68   $1,127.60   $1,127.80