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 $208.29   12.295%   $233.8993   $233.90   $233.90   $233.90  
  Purchase #2 $95.26   7.696%   $102.5912   $102.59   $102.60   $102.60  
  Purchase #3 $223.46   3.818%   $231.9917   $231.99   $232.00   $232.00  
  Purchase #4 $94.86   11.321%   $105.5991   $105.60   $105.60   $105.60  
  Purchase #5 $246.47   12.286%   $276.7513   $276.75   $276.75   $276.80  
  Purchase #6 $166.71   10.386%   $184.0245   $184.02   $184.00   $184.00  
  Purchase #7 $203.75   7.704%   $219.4469   $219.45   $219.45   $219.40  
  7 purchase totals = $1,238.80       $1,354.3040   $1,354.30   $1,354.30   $1,354.30