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 $58.31   8.796%   $63.4389   $63.44   $63.45   $63.40  
  Purchase #2 $84.84   13.278%   $96.1051   $96.11   $96.10   $96.10  
  Purchase #3 $62.87   11.605%   $70.1661   $70.17   $70.15   $70.20  
  Purchase #4 $88.33   8.646%   $95.967   $95.97   $95.95   $96.00  
  Purchase #5 $124.95   9.312%   $136.5853   $136.59   $136.60   $136.60  
  Purchase #6 $117.30   12.282%   $131.7068   $131.71   $131.70   $131.70  
  Purchase #7 $74.95   13.464%   $85.0413   $85.04   $85.05   $85.00  
  7 purchase totals = $611.55       $679.0105   $679.03   $679.00   $679.00