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 $31.71   6.662%   $33.8225   $33.82   $33.80   $33.80  
  Purchase #2 $207.37   4.123%   $215.9199   $215.92   $215.90   $215.90  
  Purchase #3 $43.74   13.461%   $49.6278   $49.63   $49.65   $49.60  
  Purchase #4 $62.78   9.689%   $68.8628   $68.86   $68.85   $68.90  
  Purchase #5 $108.70   9.457%   $118.9798   $118.98   $119.00   $119.00  
  Purchase #6 $12.41   5.476%   $13.0896   $13.09   $13.10   $13.10  
  Purchase #7 $192.35   10.110%   $211.7966   $211.80   $211.80   $211.80  
  7 purchase totals = $659.06       $712.0990   $712.10   $712.10   $712.10