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 $112.82   12.596%   $127.0308   $127.03   $127.05   $127.00  
  Purchase #2 $148.57   3.647%   $153.9883   $153.99   $154.00   $154.00  
  Purchase #3 $110.92   9.642%   $121.6149   $121.61   $121.60   $121.60  
  Purchase #4 $103.27   9.430%   $113.0084   $113.01   $113.00   $113.00  
  Purchase #5 $23.38   6.523%   $24.9051   $24.91   $24.90   $24.90  
  Purchase #6 $224.27   12.358%   $251.9853   $251.99   $252.00   $252.00  
  Purchase #7 $182.98   9.407%   $200.1929   $200.19   $200.20   $200.20  
  7 purchase totals = $906.21       $992.7257   $992.73   $992.75   $992.70