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 $218.97   11.616%   $244.4056   $244.41   $244.40   $244.40  
  Purchase #2 $204.81   3.819%   $212.6317   $212.63   $212.65   $212.60  
  Purchase #3 $41.97   8.653%   $45.6017   $45.60   $45.60   $45.60  
  Purchase #4 $40.79   3.554%   $42.2397   $42.24   $42.25   $42.20  
  Purchase #5 $30.34   5.356%   $31.965   $31.97   $31.95   $32.00  
  Purchase #6 $163.77   7.561%   $176.1526   $176.15   $176.15   $176.20  
  Purchase #7 $227.31   7.739%   $244.9015   $244.90   $244.90   $244.90  
  7 purchase totals = $927.96       $997.8978   $997.90   $997.90   $997.90