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 $213.91   13.767%   $243.359   $243.36   $243.35   $243.40  
  Purchase #2 $68.39   13.496%   $77.6199   $77.62   $77.60   $77.60  
  Purchase #3 $247.31   10.534%   $273.3616   $273.36   $273.35   $273.40  
  Purchase #4 $230.94   5.151%   $242.8357   $242.84   $242.85   $242.80  
  Purchase #5 $143.70   9.361%   $157.1518   $157.15   $157.15   $157.20  
  Purchase #6 $185.73   13.251%   $210.3411   $210.34   $210.35   $210.30  
  Purchase #7 $79.58   13.644%   $90.4379   $90.44   $90.45   $90.40  
  7 purchase totals = $1,169.56       $1,295.1070   $1,295.11   $1,295.10   $1,295.10