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 $77.25   12.147%   $86.6336   $86.63   $86.65   $86.60  
  Purchase #2 $135.30   4.365%   $141.2058   $141.21   $141.20   $141.20  
  Purchase #3 $179.48   12.116%   $201.2258   $201.23   $201.25   $201.20  
  Purchase #4 $135.41   13.376%   $153.5224   $153.52   $153.50   $153.50  
  Purchase #5 $193.30   9.849%   $212.3381   $212.34   $212.35   $212.30  
  Purchase #6 $63.29   13.741%   $71.9867   $71.99   $72.00   $72.00  
  Purchase #7 $88.73   4.561%   $92.777   $92.78   $92.80   $92.80  
  7 purchase totals = $872.76       $959.6894   $959.70   $959.75   $959.60