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 $106.26   5.362%   $111.9577   $111.96   $111.95   $112.00  
  Purchase #2 $118.43   5.248%   $124.6452   $124.65   $124.65   $124.60  
  Purchase #3 $102.66   6.202%   $109.027   $109.03   $109.05   $109.00  
  Purchase #4 $250.76   11.602%   $279.8532   $279.85   $279.85   $279.90  
  Purchase #5 $11.57   9.422%   $12.6601   $12.66   $12.65   $12.70  
  Purchase #6 $229.96   5.858%   $243.4311   $243.43   $243.45   $243.40  
  Purchase #7 $163.84   13.524%   $185.9977   $186.00   $186.00   $186.00  
  7 purchase totals = $983.48       $1,067.5720   $1,067.58   $1,067.60   $1,067.60