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 $84.79   8.819%   $92.2676   $92.27   $92.25   $92.30  
  Purchase #2 $115.57   7.839%   $124.6295   $124.63   $124.65   $124.60  
  Purchase #3 $88.34   6.695%   $94.2544   $94.25   $94.25   $94.30  
  Purchase #4 $214.63   9.646%   $235.3332   $235.33   $235.35   $235.30  
  Purchase #5 $25.36   11.796%   $28.3515   $28.35   $28.35   $28.40  
  Purchase #6 $20.95   12.442%   $23.5566   $23.56   $23.55   $23.60  
  Purchase #7 $175.64   12.792%   $198.1079   $198.11   $198.10   $198.10  
  7 purchase totals = $725.28       $796.5007   $796.50   $796.50   $796.60