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 $127.25   6.270%   $135.2286   $135.23   $135.25   $135.20  
  Purchase #2 $66.41   9.282%   $72.5742   $72.57   $72.55   $72.60  
  Purchase #3 $101.93   13.839%   $116.0361   $116.04   $116.05   $116.00  
  Purchase #4 $183.64   5.719%   $194.1424   $194.14   $194.15   $194.10  
  Purchase #5 $203.35   3.759%   $210.9939   $210.99   $211.00   $211.00  
  Purchase #6 $201.89   7.724%   $217.484   $217.48   $217.50   $217.50  
  Purchase #7 $15.36   7.765%   $16.5527   $16.55   $16.55   $16.60  
  7 purchase totals = $899.83       $963.0119   $963.00   $963.05   $963.00