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 $103.61   13.356%   $117.4482   $117.45   $117.45   $117.40  
  Purchase #2 $147.86   13.290%   $167.5106   $167.51   $167.50   $167.50  
  Purchase #3 $72.47   6.652%   $77.2907   $77.29   $77.30   $77.30  
  Purchase #4 $124.30   8.285%   $134.5983   $134.60   $134.60   $134.60  
  Purchase #5 $249.60   6.816%   $266.6127   $266.61   $266.60   $266.60  
  Purchase #6 $179.27   8.606%   $194.698   $194.70   $194.70   $194.70  
  Purchase #7 $210.78   6.280%   $224.017   $224.02   $224.00   $224.00  
  7 purchase totals = $1,087.89       $1,182.1755   $1,182.18   $1,182.15   $1,182.10