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 $176.48   11.674%   $197.0823   $197.08   $197.10   $197.10  
  Purchase #2 $55.63   6.695%   $59.3544   $59.35   $59.35   $59.40  
  Purchase #3 $166.74   9.587%   $182.7254   $182.73   $182.75   $182.70  
  Purchase #4 $187.78   9.460%   $205.544   $205.54   $205.55   $205.50  
  Purchase #5 $226.98   13.702%   $258.0808   $258.08   $258.10   $258.10  
  Purchase #6 $127.97   6.187%   $135.8875   $135.89   $135.90   $135.90  
  Purchase #7 $182.88   10.476%   $202.0385   $202.04   $202.05   $202.00  
  7 purchase totals = $1,124.46       $1,240.7129   $1,240.71   $1,240.80   $1,240.70