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 $148.34   11.144%   $164.871   $164.87   $164.85   $164.90  
  Purchase #2 $199.67   11.831%   $223.293   $223.29   $223.30   $223.30  
  Purchase #3 $120.84   11.496%   $134.7318   $134.73   $134.75   $134.70  
  Purchase #4 $174.63   7.225%   $187.247   $187.25   $187.25   $187.20  
  Purchase #5 $138.62   11.835%   $155.0257   $155.03   $155.05   $155.00  
  Purchase #6 $48.53   5.115%   $51.0123   $51.01   $51.00   $51.00  
  Purchase #7 $153.64   10.744%   $170.1471   $170.15   $170.15   $170.10  
  7 purchase totals = $984.27       $1,086.3279   $1,086.33   $1,086.35   $1,086.20