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 $64.33   7.198%   $68.9605   $68.96   $68.95   $69.00  
  Purchase #2 $80.85   6.614%   $86.1974   $86.20   $86.20   $86.20  
  Purchase #3 $120.92   12.768%   $136.3591   $136.36   $136.35   $136.40  
  Purchase #4 $34.98   10.470%   $38.6424   $38.64   $38.65   $38.60  
  Purchase #5 $231.33   6.205%   $245.684   $245.68   $245.70   $245.70  
  Purchase #6 $168.75   12.206%   $189.3476   $189.35   $189.35   $189.30  
  Purchase #7 $34.42   10.537%   $38.0468   $38.05   $38.05   $38.00  
  7 purchase totals = $735.58       $803.2378   $803.24   $803.25   $803.20