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 $93.48   3.396%   $96.6546   $96.65   $96.65   $96.70  
  Purchase #2 $232.73   10.588%   $257.3715   $257.37   $257.35   $257.40  
  Purchase #3 $210.89   3.863%   $219.0367   $219.04   $219.05   $219.00  
  Purchase #4 $85.95   6.761%   $91.7611   $91.76   $91.75   $91.80  
  Purchase #5 $164.78   13.538%   $187.0879   $187.09   $187.10   $187.10  
  Purchase #6 $204.74   5.862%   $216.7419   $216.74   $216.75   $216.70  
  Purchase #7 $117.32   4.745%   $122.8868   $122.89   $122.90   $122.90  
  7 purchase totals = $1,109.89       $1,191.5405   $1,191.54   $1,191.55   $1,191.60