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 $98.68   12.511%   $111.0259   $111.03   $111.05   $111.00  
  Purchase #2 $124.89   11.816%   $139.647   $139.65   $139.65   $139.60  
  Purchase #3 $24.27   7.463%   $26.0813   $26.08   $26.10   $26.10  
  Purchase #4 $184.51   8.534%   $200.2561   $200.26   $200.25   $200.30  
  Purchase #5 $61.61   4.704%   $64.5081   $64.51   $64.50   $64.50  
  Purchase #6 $68.73   11.615%   $76.713   $76.71   $76.70   $76.70  
  Purchase #7 $97.36   13.184%   $110.1959   $110.20   $110.20   $110.20  
  7 purchase totals = $660.05       $728.4273   $728.44   $728.45   $728.40