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 $49.39   12.872%   $55.7475   $55.75   $55.75   $55.70  
  Purchase #2 $166.31   13.621%   $188.9631   $188.96   $188.95   $189.00  
  Purchase #3 $156.96   4.819%   $164.5239   $164.52   $164.50   $164.50  
  Purchase #4 $85.58   3.681%   $88.7302   $88.73   $88.75   $88.70  
  Purchase #5 $117.45   8.214%   $127.0973   $127.10   $127.10   $127.10  
  Purchase #6 $250.54   10.676%   $277.2877   $277.29   $277.30   $277.30  
  Purchase #7 $200.90   6.794%   $214.5491   $214.55   $214.55   $214.50  
  7 purchase totals = $1,027.13       $1,116.8988   $1,116.90   $1,116.90   $1,116.80