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 $60.81   10.674%   $67.3009   $67.30   $67.30   $67.30  
  Purchase #2 $181.40   6.263%   $192.7611   $192.76   $192.75   $192.80  
  Purchase #3 $37.77   3.282%   $39.0096   $39.01   $39.00   $39.00  
  Purchase #4 $136.84   8.397%   $148.3305   $148.33   $148.35   $148.30  
  Purchase #5 $44.94   11.773%   $50.2308   $50.23   $50.25   $50.20  
  Purchase #6 $195.62   8.142%   $211.5474   $211.55   $211.55   $211.50  
  Purchase #7 $236.90   9.275%   $258.8725   $258.87   $258.85   $258.90  
  7 purchase totals = $894.28       $968.0528   $968.05   $968.05   $968.00