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 $218.34   8.398%   $236.6762   $236.68   $236.70   $236.70  
  Purchase #2 $26.37   3.489%   $27.29   $27.29   $27.30   $27.30  
  Purchase #3 $211.52   3.629%   $219.1961   $219.20   $219.20   $219.20  
  Purchase #4 $237.26   3.253%   $244.9781   $244.98   $245.00   $245.00  
  Purchase #5 $69.92   9.565%   $76.6078   $76.61   $76.60   $76.60  
  Purchase #6 $81.98   9.212%   $89.532   $89.53   $89.55   $89.50  
  Purchase #7 $26.41   12.314%   $29.6621   $29.66   $29.65   $29.70  
  7 purchase totals = $871.80       $923.9423   $923.95   $924.00   $924.00