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 $58.26   12.194%   $65.3642   $65.36   $65.35   $65.40  
  Purchase #2 $250.31   8.337%   $271.1783   $271.18   $271.20   $271.20  
  Purchase #3 $153.30   7.128%   $164.2272   $164.23   $164.25   $164.20  
  Purchase #4 $184.55   9.341%   $201.7888   $201.79   $201.80   $201.80  
  Purchase #5 $43.68   11.500%   $48.7032   $48.70   $48.70   $48.70  
  Purchase #6 $64.85   10.235%   $71.4874   $71.49   $71.50   $71.50  
  Purchase #7 $221.81   10.561%   $245.2354   $245.24   $245.25   $245.20  
  7 purchase totals = $976.76       $1,067.9845   $1,067.99   $1,068.05   $1,068.00