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 $176.69   12.562%   $198.8858   $198.89   $198.90   $198.90  
  Purchase #2 $177.26   4.223%   $184.7457   $184.75   $184.75   $184.70  
  Purchase #3 $127.36   7.770%   $137.2559   $137.26   $137.25   $137.30  
  Purchase #4 $58.52   9.338%   $63.9846   $63.98   $64.00   $64.00  
  Purchase #5 $92.99   3.434%   $96.1833   $96.18   $96.20   $96.20  
  Purchase #6 $191.65   5.722%   $202.6162   $202.62   $202.60   $202.60  
  Purchase #7 $152.63   7.843%   $164.6008   $164.60   $164.60   $164.60  
  7 purchase totals = $977.10       $1,048.2723   $1,048.28   $1,048.30   $1,048.30