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 $49.41   7.339%   $53.0362   $53.04   $53.05   $53.00  
  Purchase #2 $191.59   4.701%   $200.5966   $200.60   $200.60   $200.60  
  Purchase #3 $245.87   6.637%   $262.1884   $262.19   $262.20   $262.20  
  Purchase #4 $158.93   5.333%   $167.4057   $167.41   $167.40   $167.40  
  Purchase #5 $7.74   10.153%   $8.5258   $8.53   $8.55   $8.50  
  Purchase #6 $179.56   13.318%   $203.4738   $203.47   $203.45   $203.50  
  Purchase #7 $244.74   5.836%   $259.023   $259.02   $259.00   $259.00  
  7 purchase totals = $1,077.84       $1,154.2495   $1,154.26   $1,154.25   $1,154.20