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 $222.39   13.578%   $252.5861   $252.59   $252.60   $252.60  
  Purchase #2 $119.49   4.562%   $124.9411   $124.94   $124.95   $124.90  
  Purchase #3 $176.87   11.628%   $197.4364   $197.44   $197.45   $197.40  
  Purchase #4 $41.52   8.640%   $45.1073   $45.11   $45.10   $45.10  
  Purchase #5 $114.48   8.492%   $124.2016   $124.20   $124.20   $124.20  
  Purchase #6 $192.36   12.722%   $216.832   $216.83   $216.85   $216.80  
  Purchase #7 $60.91   6.616%   $64.9398   $64.94   $64.95   $64.90  
  7 purchase totals = $928.02       $1,026.0443   $1,026.05   $1,026.10   $1,025.90