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 $216.88   8.560%   $235.4449   $235.44   $235.45   $235.40  
  Purchase #2 $17.41   9.464%   $19.0577   $19.06   $19.05   $19.10  
  Purchase #3 $71.84   7.631%   $77.3221   $77.32   $77.30   $77.30  
  Purchase #4 $197.94   6.603%   $211.01   $211.01   $211.00   $211.00  
  Purchase #5 $208.44   10.654%   $230.6472   $230.65   $230.65   $230.60  
  Purchase #6 $82.80   5.329%   $87.2124   $87.21   $87.20   $87.20  
  Purchase #7 $204.62   5.175%   $215.2091   $215.21   $215.20   $215.20  
  7 purchase totals = $999.93       $1,075.9034   $1,075.90   $1,075.85   $1,075.80