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 $84.54   9.701%   $92.7412   $92.74   $92.75   $92.70  
  Purchase #2 $49.77   13.676%   $56.5765   $56.58   $56.60   $56.60  
  Purchase #3 $37.64   8.239%   $40.7412   $40.74   $40.75   $40.70  
  Purchase #4 $98.44   3.663%   $102.0459   $102.05   $102.05   $102.00  
  Purchase #5 $223.70   10.118%   $246.334   $246.33   $246.35   $246.30  
  Purchase #6 $249.50   5.414%   $263.0079   $263.01   $263.00   $263.00  
  Purchase #7 $23.68   10.467%   $26.1586   $26.16   $26.15   $26.20  
  7 purchase totals = $767.27       $827.6053   $827.61   $827.65   $827.50