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 $198.95   13.523%   $225.854   $225.85   $225.85   $225.90  
  Purchase #2 $90.96   5.355%   $95.8309   $95.83   $95.85   $95.80  
  Purchase #3 $121.67   3.397%   $125.8031   $125.80   $125.80   $125.80  
  Purchase #4 $178.46   4.388%   $186.2908   $186.29   $186.30   $186.30  
  Purchase #5 $197.77   8.208%   $214.003   $214.00   $214.00   $214.00  
  Purchase #6 $11.85   9.571%   $12.9842   $12.98   $13.00   $13.00  
  Purchase #7 $245.91   12.219%   $275.9577   $275.96   $275.95   $276.00  
  7 purchase totals = $1,045.57       $1,136.7237   $1,136.71   $1,136.75   $1,136.80