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 $127.61   6.791%   $136.276   $136.28   $136.30   $136.30  
  Purchase #2 $88.55   3.841%   $91.9512   $91.95   $91.95   $92.00  
  Purchase #3 $30.32   3.195%   $31.2887   $31.29   $31.30   $31.30  
  Purchase #4 $50.62   10.762%   $56.0677   $56.07   $56.05   $56.10  
  Purchase #5 $68.72   10.612%   $76.0126   $76.01   $76.00   $76.00  
  Purchase #6 $188.36   6.716%   $201.0103   $201.01   $201.00   $201.00  
  Purchase #7 $210.69   11.109%   $234.0956   $234.10   $234.10   $234.10  
  7 purchase totals = $764.87       $826.7021   $826.71   $826.70   $826.80