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 $109.98   8.795%   $119.6527   $119.65   $119.65   $119.70  
  Purchase #2 $106.35   11.425%   $118.5005   $118.50   $118.50   $118.50  
  Purchase #3 $242.72   9.672%   $266.1959   $266.20   $266.20   $266.20  
  Purchase #4 $246.31   6.560%   $262.4679   $262.47   $262.45   $262.50  
  Purchase #5 $55.41   13.806%   $63.0599   $63.06   $63.05   $63.10  
  Purchase #6 $111.50   11.482%   $124.3024   $124.30   $124.30   $124.30  
  Purchase #7 $19.72   13.153%   $22.3138   $22.31   $22.30   $22.30  
  7 purchase totals = $891.99       $976.4931   $976.49   $976.45   $976.60