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 $69.72   8.489%   $75.6385   $75.64   $75.65   $75.60  
  Purchase #2 $83.91   11.505%   $93.5638   $93.56   $93.55   $93.60  
  Purchase #3 $173.68   10.552%   $192.0067   $192.01   $192.00   $192.00  
  Purchase #4 $146.45   7.372%   $157.2463   $157.25   $157.25   $157.20  
  Purchase #5 $237.35   12.102%   $266.0741   $266.07   $266.05   $266.10  
  Purchase #6 $23.36   13.609%   $26.5391   $26.54   $26.55   $26.50  
  Purchase #7 $232.57   5.847%   $246.1684   $246.17   $246.15   $246.20  
  7 purchase totals = $967.04       $1,057.2369   $1,057.24   $1,057.20   $1,057.20