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 $46.88   11.551%   $52.2951   $52.30   $52.30   $52.30  
  Purchase #2 $202.88   13.173%   $229.6054   $229.61   $229.60   $229.60  
  Purchase #3 $161.72   13.827%   $184.081   $184.08   $184.10   $184.10  
  Purchase #4 $213.26   5.208%   $224.3666   $224.37   $224.35   $224.40  
  Purchase #5 $61.82   3.588%   $64.0381   $64.04   $64.05   $64.00  
  Purchase #6 $14.78   6.591%   $15.7541   $15.75   $15.75   $15.80  
  Purchase #7 $113.70   9.110%   $124.0581   $124.06   $124.05   $124.10  
  7 purchase totals = $815.04       $894.1984   $894.21   $894.20   $894.30