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 $137.68   10.525%   $152.1708   $152.17   $152.15   $152.20  
  Purchase #2 $211.98   9.542%   $232.2071   $232.21   $232.20   $232.20  
  Purchase #3 $81.42   12.423%   $91.5348   $91.53   $91.55   $91.50  
  Purchase #4 $186.26   4.715%   $195.0422   $195.04   $195.05   $195.00  
  Purchase #5 $38.55   11.707%   $43.063   $43.06   $43.05   $43.10  
  Purchase #6 $176.66   4.855%   $185.2368   $185.24   $185.25   $185.20  
  Purchase #7 $152.52   11.788%   $170.4991   $170.50   $170.50   $170.50  
  7 purchase totals = $985.07       $1,069.7538   $1,069.75   $1,069.75   $1,069.70