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 $201.43   10.186%   $221.9477   $221.95   $221.95   $221.90  
  Purchase #2 $64.83   4.229%   $67.5717   $67.57   $67.55   $67.60  
  Purchase #3 $29.27   3.865%   $30.4013   $30.40   $30.40   $30.40  
  Purchase #4 $189.42   9.266%   $206.9717   $206.97   $206.95   $207.00  
  Purchase #5 $208.96   8.549%   $226.824   $226.82   $226.80   $226.80  
  Purchase #6 $9.28   8.574%   $10.0757   $10.08   $10.10   $10.10  
  Purchase #7 $197.97   6.746%   $211.3251   $211.33   $211.35   $211.30  
  7 purchase totals = $901.16       $975.1172   $975.12   $975.10   $975.10