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 $181.65   11.511%   $202.5597   $202.56   $202.55   $202.60  
  Purchase #2 $131.31   6.586%   $139.9581   $139.96   $139.95   $140.00  
  Purchase #3 $19.51   12.144%   $21.8793   $21.88   $21.90   $21.90  
  Purchase #4 $228.72   7.856%   $246.6882   $246.69   $246.70   $246.70  
  Purchase #5 $91.44   9.832%   $100.4304   $100.43   $100.45   $100.40  
  Purchase #6 $107.44   9.661%   $117.8198   $117.82   $117.80   $117.80  
  Purchase #7 $168.97   3.658%   $175.1509   $175.15   $175.15   $175.20  
  7 purchase totals = $929.04       $1,004.4864   $1,004.49   $1,004.50   $1,004.60