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 $203.51   4.123%   $211.9007   $211.90   $211.90   $211.90  
  Purchase #2 $246.71   8.171%   $266.8687   $266.87   $266.85   $266.90  
  Purchase #3 $26.66   13.711%   $30.3154   $30.32   $30.30   $30.30  
  Purchase #4 $165.31   4.721%   $173.1143   $173.11   $173.10   $173.10  
  Purchase #5 $70.58   4.392%   $73.6799   $73.68   $73.70   $73.70  
  Purchase #6 $110.29   6.283%   $117.2195   $117.22   $117.20   $117.20  
  Purchase #7 $59.61   12.159%   $66.858   $66.86   $66.85   $66.90  
  7 purchase totals = $882.67       $939.9565   $939.96   $939.90   $940.00