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 $88.84   10.285%   $97.9772   $97.98   $98.00   $98.00  
  Purchase #2 $96.92   4.137%   $100.9296   $100.93   $100.95   $100.90  
  Purchase #3 $51.85   7.836%   $55.913   $55.91   $55.90   $55.90  
  Purchase #4 $218.90   3.736%   $227.0781   $227.08   $227.10   $227.10  
  Purchase #5 $234.83   3.570%   $243.2134   $243.21   $243.20   $243.20  
  Purchase #6 $69.51   3.587%   $72.0033   $72.00   $72.00   $72.00  
  Purchase #7 $67.45   5.120%   $70.9034   $70.90   $70.90   $70.90  
  7 purchase totals = $828.30       $868.0180   $868.01   $868.05   $868.00