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 $57.31   10.249%   $63.1837   $63.18   $63.20   $63.20  
  Purchase #2 $5.82   13.826%   $6.6247   $6.62   $6.60   $6.60  
  Purchase #3 $238.26   13.189%   $269.6841   $269.68   $269.70   $269.70  
  Purchase #4 $168.62   5.288%   $177.5366   $177.54   $177.55   $177.50  
  Purchase #5 $195.91   10.549%   $216.5765   $216.58   $216.60   $216.60  
  Purchase #6 $93.78   8.784%   $102.0176   $102.02   $102.00   $102.00  
  Purchase #7 $38.34   7.247%   $41.1185   $41.12   $41.10   $41.10  
  7 purchase totals = $798.04       $876.7417   $876.74   $876.75   $876.70