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 $231.66   9.625%   $253.9573   $253.96   $253.95   $254.00  
  Purchase #2 $136.88   4.468%   $142.9958   $143.00   $143.00   $143.00  
  Purchase #3 $200.75   4.824%   $210.4342   $210.43   $210.45   $210.40  
  Purchase #4 $60.26   5.295%   $63.4508   $63.45   $63.45   $63.50  
  Purchase #5 $134.84   6.760%   $143.9552   $143.96   $143.95   $144.00  
  Purchase #6 $30.81   13.797%   $35.0609   $35.06   $35.05   $35.10  
  Purchase #7 $22.86   13.861%   $26.0286   $26.03   $26.05   $26.00  
  7 purchase totals = $818.06       $875.8828   $875.89   $875.90   $876.00