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 $189.92   6.683%   $202.6124   $202.61   $202.60   $202.60  
  Purchase #2 $188.92   11.351%   $210.3643   $210.36   $210.35   $210.40  
  Purchase #3 $205.56   6.637%   $219.203   $219.20   $219.20   $219.20  
  Purchase #4 $248.89   3.849%   $258.4698   $258.47   $258.45   $258.50  
  Purchase #5 $150.67   10.783%   $166.9167   $166.92   $166.90   $166.90  
  Purchase #6 $26.45   8.333%   $28.6541   $28.65   $28.65   $28.70  
  Purchase #7 $13.79   13.742%   $15.685   $15.69   $15.70   $15.70  
  7 purchase totals = $1,024.20       $1,101.9053   $1,101.90   $1,101.85   $1,102.00