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 $88.83   4.311%   $92.6595   $92.66   $92.65   $92.70  
  Purchase #2 $241.75   8.458%   $262.1972   $262.20   $262.20   $262.20  
  Purchase #3 $163.67   8.454%   $177.5067   $177.51   $177.50   $177.50  
  Purchase #4 $171.44   5.345%   $180.6035   $180.60   $180.60   $180.60  
  Purchase #5 $45.78   5.486%   $48.2915   $48.29   $48.30   $48.30  
  Purchase #6 $103.54   6.306%   $110.0692   $110.07   $110.05   $110.10  
  Purchase #7 $115.68   10.351%   $127.654   $127.65   $127.65   $127.70  
  7 purchase totals = $930.69       $998.9816   $998.98   $998.95   $999.10