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 $123.86   9.828%   $136.033   $136.03   $136.05   $136.00  
  Purchase #2 $121.60   4.380%   $126.9261   $126.93   $126.95   $126.90  
  Purchase #3 $13.80   5.262%   $14.5262   $14.53   $14.55   $14.50  
  Purchase #4 $196.56   3.323%   $203.0917   $203.09   $203.10   $203.10  
  Purchase #5 $50.98   4.202%   $53.1222   $53.12   $53.10   $53.10  
  Purchase #6 $136.57   8.695%   $148.4448   $148.44   $148.45   $148.40  
  Purchase #7 $158.68   5.687%   $167.7041   $167.70   $167.70   $167.70  
  7 purchase totals = $802.05       $849.8481   $849.84   $849.90   $849.70