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 $166.97   10.221%   $184.036   $184.04   $184.05   $184.00  
  Purchase #2 $46.44   8.411%   $50.3461   $50.35   $50.35   $50.30  
  Purchase #3 $211.89   9.120%   $231.2144   $231.21   $231.20   $231.20  
  Purchase #4 $34.94   13.134%   $39.529   $39.53   $39.55   $39.50  
  Purchase #5 $222.81   12.836%   $251.4099   $251.41   $251.40   $251.40  
  Purchase #6 $125.49   13.370%   $142.268   $142.27   $142.25   $142.30  
  Purchase #7 $44.67   5.436%   $47.0983   $47.10   $47.10   $47.10  
  7 purchase totals = $853.21       $945.9017   $945.91   $945.90   $945.80