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 $242.50   10.332%   $267.5551   $267.56   $267.55   $267.60  
  Purchase #2 $38.98   12.837%   $43.9839   $43.98   $44.00   $44.00  
  Purchase #3 $82.82   6.822%   $88.47   $88.47   $88.45   $88.50  
  Purchase #4 $249.75   5.768%   $264.1556   $264.16   $264.15   $264.20  
  Purchase #5 $50.72   5.590%   $53.5552   $53.56   $53.55   $53.60  
  Purchase #6 $95.29   3.812%   $98.9225   $98.92   $98.90   $98.90  
  Purchase #7 $194.93   5.402%   $205.4601   $205.46   $205.45   $205.50  
  7 purchase totals = $954.99       $1,022.1024   $1,022.11   $1,022.05   $1,022.30