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 $17.28   8.677%   $18.7794   $18.78   $18.80   $18.80  
  Purchase #2 $123.35   3.850%   $128.099   $128.10   $128.10   $128.10  
  Purchase #3 $193.31   8.552%   $209.8419   $209.84   $209.85   $209.80  
  Purchase #4 $57.68   12.745%   $65.0313   $65.03   $65.05   $65.00  
  Purchase #5 $74.55   12.385%   $83.783   $83.78   $83.80   $83.80  
  Purchase #6 $101.28   12.354%   $113.7921   $113.79   $113.80   $113.80  
  Purchase #7 $115.27   10.833%   $127.7572   $127.76   $127.75   $127.80  
  7 purchase totals = $682.72       $747.0839   $747.08   $747.15   $747.10