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 $9.28   7.690%   $9.9936   $9.99   $10.00   $10.00  
  Purchase #2 $113.87   9.572%   $124.7696   $124.77   $124.75   $124.80  
  Purchase #3 $69.75   13.281%   $79.0135   $79.01   $79.00   $79.00  
  Purchase #4 $112.41   13.619%   $127.7191   $127.72   $127.70   $127.70  
  Purchase #5 $40.46   10.837%   $44.8447   $44.84   $44.85   $44.80  
  Purchase #6 $39.41   11.254%   $43.8452   $43.85   $43.85   $43.80  
  Purchase #7 $179.95   7.220%   $192.9424   $192.94   $192.95   $192.90  
  7 purchase totals = $565.13       $623.1281   $623.12   $623.10   $623.00