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 $118.42   13.185%   $134.0337   $134.03   $134.05   $134.00  
  Purchase #2 $241.72   3.708%   $250.683   $250.68   $250.70   $250.70  
  Purchase #3 $72.39   7.651%   $77.9286   $77.93   $77.95   $77.90  
  Purchase #4 $177.26   6.335%   $188.4894   $188.49   $188.50   $188.50  
  Purchase #5 $151.34   8.755%   $164.5898   $164.59   $164.60   $164.60  
  Purchase #6 $40.56   3.360%   $41.9228   $41.92   $41.90   $41.90  
  Purchase #7 $236.27   13.377%   $267.8758   $267.88   $267.90   $267.90  
  7 purchase totals = $1,037.96       $1,125.5231   $1,125.52   $1,125.60   $1,125.50