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 $207.29   9.783%   $227.5692   $227.57   $227.55   $227.60  
  Purchase #2 $181.75   6.690%   $193.9091   $193.91   $193.90   $193.90  
  Purchase #3 $239.69   5.351%   $252.5158   $252.52   $252.50   $252.50  
  Purchase #4 $212.44   8.366%   $230.2127   $230.21   $230.20   $230.20  
  Purchase #5 $32.57   4.237%   $33.95   $33.95   $33.95   $34.00  
  Purchase #6 $42.47   7.415%   $45.6192   $45.62   $45.60   $45.60  
  Purchase #7 $215.84   6.693%   $230.2862   $230.29   $230.30   $230.30  
  7 purchase totals = $1,132.05       $1,214.0622   $1,214.07   $1,214.00   $1,214.10