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 $82.49   10.629%   $91.2579   $91.26   $91.25   $91.30  
  Purchase #2 $53.58   12.215%   $60.1248   $60.12   $60.10   $60.10  
  Purchase #3 $209.45   3.235%   $216.2257   $216.23   $216.25   $216.20  
  Purchase #4 $240.31   8.411%   $260.5225   $260.52   $260.50   $260.50  
  Purchase #5 $34.92   5.650%   $36.893   $36.89   $36.90   $36.90  
  Purchase #6 $66.72   9.144%   $72.8209   $72.82   $72.80   $72.80  
  Purchase #7 $55.27   10.726%   $61.1983   $61.20   $61.20   $61.20  
  7 purchase totals = $742.74       $799.0431   $799.04   $799.00   $799.00