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 $66.45   11.811%   $74.2984   $74.30   $74.30   $74.30  
  Purchase #2 $99.34   6.383%   $105.6809   $105.68   $105.70   $105.70  
  Purchase #3 $87.30   7.617%   $93.9496   $93.95   $93.95   $93.90  
  Purchase #4 $193.86   9.832%   $212.9203   $212.92   $212.90   $212.90  
  Purchase #5 $49.83   7.526%   $53.5802   $53.58   $53.60   $53.60  
  Purchase #6 $5.45   12.624%   $6.138   $6.14   $6.15   $6.10  
  Purchase #7 $71.56   10.849%   $79.3235   $79.32   $79.30   $79.30  
  7 purchase totals = $573.79       $625.8909   $625.89   $625.90   $625.80