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 $167.76   8.500%   $182.0196   $182.02   $182.00   $182.00  
  Purchase #2 $101.99   4.769%   $106.8539   $106.85   $106.85   $106.90  
  Purchase #3 $184.39   9.863%   $202.5764   $202.58   $202.60   $202.60  
  Purchase #4 $229.54   4.277%   $239.3574   $239.36   $239.35   $239.40  
  Purchase #5 $117.79   11.708%   $131.5809   $131.58   $131.60   $131.60  
  Purchase #6 $35.47   13.124%   $40.1251   $40.13   $40.15   $40.10  
  Purchase #7 $138.59   6.476%   $147.5651   $147.57   $147.55   $147.60  
  7 purchase totals = $975.53       $1,050.0784   $1,050.09   $1,050.10   $1,050.20