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 $226.47   6.533%   $241.2653   $241.27   $241.25   $241.30  
  Purchase #2 $155.46   11.782%   $173.7763   $173.78   $173.80   $173.80  
  Purchase #3 $234.40   13.594%   $266.2643   $266.26   $266.25   $266.30  
  Purchase #4 $130.56   4.775%   $136.7942   $136.79   $136.80   $136.80  
  Purchase #5 $11.78   9.321%   $12.878   $12.88   $12.90   $12.90  
  Purchase #6 $91.25   4.850%   $95.6756   $95.68   $95.70   $95.70  
  Purchase #7 $65.93   3.110%   $67.9804   $67.98   $68.00   $68.00  
  7 purchase totals = $915.85       $994.6341   $994.64   $994.70   $994.80