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 $191.86   8.609%   $208.3772   $208.38   $208.40   $208.40  
  Purchase #2 $142.43   5.495%   $150.2565   $150.26   $150.25   $150.30  
  Purchase #3 $98.25   13.775%   $111.7839   $111.78   $111.80   $111.80  
  Purchase #4 $249.35   7.270%   $267.4777   $267.48   $267.50   $267.50  
  Purchase #5 $167.94   4.273%   $175.1161   $175.12   $175.10   $175.10  
  Purchase #6 $16.40   3.479%   $16.9706   $16.97   $16.95   $17.00  
  Purchase #7 $126.68   6.827%   $135.3284   $135.33   $135.35   $135.30  
  7 purchase totals = $992.91       $1,065.3104   $1,065.32   $1,065.35   $1,065.40