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 $61.32   7.555%   $65.9527   $65.95   $65.95   $66.00  
  Purchase #2 $111.97   5.619%   $118.2616   $118.26   $118.25   $118.30  
  Purchase #3 $104.57   12.122%   $117.246   $117.25   $117.25   $117.20  
  Purchase #4 $100.68   7.436%   $108.1666   $108.17   $108.15   $108.20  
  Purchase #5 $22.35   10.171%   $24.6232   $24.62   $24.60   $24.60  
  Purchase #6 $174.82   6.839%   $186.7759   $186.78   $186.80   $186.80  
  Purchase #7 $189.70   11.635%   $211.7716   $211.77   $211.75   $211.80  
  7 purchase totals = $765.41       $832.7976   $832.80   $832.75   $832.90