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 $198.66   3.224%   $205.0648   $205.06   $205.05   $205.10  
  Purchase #2 $212.33   13.409%   $240.8013   $240.80   $240.80   $240.80  
  Purchase #3 $159.81   10.686%   $176.8873   $176.89   $176.90   $176.90  
  Purchase #4 $121.42   5.761%   $128.415   $128.42   $128.40   $128.40  
  Purchase #5 $82.81   10.489%   $91.4959   $91.50   $91.50   $91.50  
  Purchase #6 $239.35   13.517%   $271.7029   $271.70   $271.70   $271.70  
  Purchase #7 $166.64   13.537%   $189.1981   $189.20   $189.20   $189.20  
  7 purchase totals = $1,181.02       $1,303.5653   $1,303.57   $1,303.55   $1,303.60