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 $61.78   3.815%   $64.1369   $64.14   $64.15   $64.10  
  Purchase #2 $191.89   5.673%   $202.7759   $202.78   $202.80   $202.80  
  Purchase #3 $38.63   11.258%   $42.979   $42.98   $43.00   $43.00  
  Purchase #4 $242.62   5.767%   $256.6119   $256.61   $256.60   $256.60  
  Purchase #5 $162.74   11.247%   $181.0434   $181.04   $181.05   $181.00  
  Purchase #6 $226.71   6.472%   $241.3827   $241.38   $241.40   $241.40  
  Purchase #7 $15.56   4.377%   $16.2411   $16.24   $16.25   $16.20  
  7 purchase totals = $939.93       $1,005.1709   $1,005.17   $1,005.25   $1,005.10