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 $54.68   6.197%   $58.0685   $58.07   $58.05   $58.10  
  Purchase #2 $230.96   8.690%   $251.0304   $251.03   $251.05   $251.00  
  Purchase #3 $173.63   4.792%   $181.9503   $181.95   $181.95   $182.00  
  Purchase #4 $241.94   6.103%   $256.7056   $256.71   $256.70   $256.70  
  Purchase #5 $87.41   9.201%   $95.4526   $95.45   $95.45   $95.50  
  Purchase #6 $57.94   7.280%   $62.158   $62.16   $62.15   $62.20  
  Purchase #7 $117.76   8.413%   $127.6671   $127.67   $127.65   $127.70  
  7 purchase totals = $964.32       $1,033.0325   $1,033.04   $1,033.00   $1,033.20