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 $53.70   13.591%   $60.9984   $61.00   $61.00   $61.00  
  Purchase #2 $129.86   3.465%   $134.3596   $134.36   $134.35   $134.40  
  Purchase #3 $142.45   3.628%   $147.6181   $147.62   $147.60   $147.60  
  Purchase #4 $81.54   9.350%   $89.164   $89.16   $89.15   $89.20  
  Purchase #5 $170.83   3.854%   $177.4138   $177.41   $177.40   $177.40  
  Purchase #6 $111.63   10.197%   $123.0129   $123.01   $123.00   $123.00  
  Purchase #7 $213.52   10.550%   $236.0464   $236.05   $236.05   $236.00  
  7 purchase totals = $903.53       $968.6132   $968.61   $968.55   $968.60