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 $195.57   6.367%   $208.0219   $208.02   $208.00   $208.00  
  Purchase #2 $67.37   8.471%   $73.0769   $73.08   $73.10   $73.10  
  Purchase #3 $194.34   11.814%   $217.2993   $217.30   $217.30   $217.30  
  Purchase #4 $158.27   5.318%   $166.6868   $166.69   $166.70   $166.70  
  Purchase #5 $64.39   11.528%   $71.8129   $71.81   $71.80   $71.80  
  Purchase #6 $100.48   5.474%   $105.9803   $105.98   $106.00   $106.00  
  Purchase #7 $246.79   7.285%   $264.7687   $264.77   $264.75   $264.80  
  7 purchase totals = $1,027.21       $1,107.6468   $1,107.65   $1,107.65   $1,107.70