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 $152.67   8.372%   $165.4515   $165.45   $165.45   $165.50  
  Purchase #2 $226.74   3.775%   $235.2994   $235.30   $235.30   $235.30  
  Purchase #3 $179.44   9.699%   $196.8439   $196.84   $196.85   $196.80  
  Purchase #4 $161.42   13.241%   $182.7936   $182.79   $182.80   $182.80  
  Purchase #5 $82.70   7.430%   $88.8446   $88.84   $88.85   $88.80  
  Purchase #6 $57.57   4.873%   $60.3754   $60.38   $60.40   $60.40  
  Purchase #7 $95.45   11.666%   $106.5852   $106.59   $106.60   $106.60  
  7 purchase totals = $955.99       $1,036.1936   $1,036.19   $1,036.25   $1,036.20