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 $235.40   11.308%   $262.019   $262.02   $262.00   $262.00  
  Purchase #2 $20.89   9.331%   $22.8392   $22.84   $22.85   $22.80  
  Purchase #3 $18.83   10.669%   $20.839   $20.84   $20.85   $20.80  
  Purchase #4 $90.66   13.663%   $103.0469   $103.05   $103.05   $103.00  
  Purchase #5 $147.37   9.314%   $161.096   $161.10   $161.10   $161.10  
  Purchase #6 $41.78   5.492%   $44.0746   $44.07   $44.05   $44.10  
  Purchase #7 $69.31   11.273%   $77.1233   $77.12   $77.10   $77.10  
  7 purchase totals = $624.24       $691.0380   $691.04   $691.00   $690.90