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 $112.81   3.736%   $117.0246   $117.02   $117.00   $117.00  
  Purchase #2 $168.75   7.427%   $181.2831   $181.28   $181.30   $181.30  
  Purchase #3 $230.75   4.780%   $241.7799   $241.78   $241.80   $241.80  
  Purchase #4 $240.42   7.743%   $259.0357   $259.04   $259.05   $259.00  
  Purchase #5 $125.87   3.700%   $130.5272   $130.53   $130.55   $130.50  
  Purchase #6 $231.78   13.450%   $262.9544   $262.95   $262.95   $263.00  
  Purchase #7 $49.58   8.372%   $53.7308   $53.73   $53.75   $53.70  
  7 purchase totals = $1,159.96       $1,246.3357   $1,246.33   $1,246.40   $1,246.30