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 $53.63   10.341%   $59.1759   $59.18   $59.20   $59.20  
  Purchase #2 $7.96   10.737%   $8.8147   $8.81   $8.80   $8.80  
  Purchase #3 $70.49   7.346%   $75.6682   $75.67   $75.65   $75.70  
  Purchase #4 $246.61   11.811%   $275.7371   $275.74   $275.75   $275.70  
  Purchase #5 $227.34   5.501%   $239.846   $239.85   $239.85   $239.80  
  Purchase #6 $25.91   6.412%   $27.5713   $27.57   $27.55   $27.60  
  Purchase #7 $217.25   5.874%   $230.0113   $230.01   $230.00   $230.00  
  7 purchase totals = $849.19       $916.8245   $916.83   $916.80   $916.80