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 $209.33   6.538%   $223.016   $223.02   $223.00   $223.00  
  Purchase #2 $29.84   8.599%   $32.4059   $32.41   $32.40   $32.40  
  Purchase #3 $58.28   10.839%   $64.597   $64.60   $64.60   $64.60  
  Purchase #4 $183.79   13.830%   $209.2082   $209.21   $209.20   $209.20  
  Purchase #5 $178.40   6.418%   $189.8497   $189.85   $189.85   $189.80  
  Purchase #6 $176.90   12.168%   $198.4252   $198.43   $198.45   $198.40  
  Purchase #7 $250.61   7.306%   $268.9196   $268.92   $268.90   $268.90  
  7 purchase totals = $1,087.15       $1,186.4216   $1,186.44   $1,186.40   $1,186.30