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 $188.93   10.276%   $208.3444   $208.34   $208.35   $208.30  
  Purchase #2 $177.54   13.124%   $200.8403   $200.84   $200.85   $200.80  
  Purchase #3 $8.51   11.750%   $9.5099   $9.51   $9.50   $9.50  
  Purchase #4 $40.51   3.514%   $41.9335   $41.93   $41.95   $41.90  
  Purchase #5 $232.76   9.171%   $254.1064   $254.11   $254.10   $254.10  
  Purchase #6 $175.36   6.220%   $186.2674   $186.27   $186.25   $186.30  
  Purchase #7 $152.41   5.477%   $160.7575   $160.76   $160.75   $160.80  
  7 purchase totals = $976.02       $1,061.7594   $1,061.76   $1,061.75   $1,061.70