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 $208.53   7.139%   $223.417   $223.42   $223.40   $223.40  
  Purchase #2 $84.46   10.873%   $93.6433   $93.64   $93.65   $93.60  
  Purchase #3 $33.46   8.144%   $36.185   $36.19   $36.20   $36.20  
  Purchase #4 $66.80   8.570%   $72.5248   $72.52   $72.50   $72.50  
  Purchase #5 $200.71   3.699%   $208.1343   $208.13   $208.15   $208.10  
  Purchase #6 $111.33   9.764%   $122.2003   $122.20   $122.20   $122.20  
  Purchase #7 $191.55   8.631%   $208.0827   $208.08   $208.10   $208.10  
  7 purchase totals = $896.84       $964.1874   $964.18   $964.20   $964.10