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 $18.49   4.860%   $19.3886   $19.39   $19.40   $19.40  
  Purchase #2 $99.52   11.761%   $111.2245   $111.22   $111.20   $111.20  
  Purchase #3 $221.84   6.430%   $236.1043   $236.10   $236.10   $236.10  
  Purchase #4 $45.62   12.574%   $51.3563   $51.36   $51.35   $51.40  
  Purchase #5 $187.57   10.553%   $207.3643   $207.36   $207.35   $207.40  
  Purchase #6 $44.94   5.629%   $47.4697   $47.47   $47.45   $47.50  
  Purchase #7 $34.78   11.564%   $38.802   $38.80   $38.80   $38.80  
  7 purchase totals = $652.76       $711.7097   $711.70   $711.65   $711.80