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 $55.37   9.873%   $60.8367   $60.84   $60.85   $60.80  
  Purchase #2 $213.47   4.636%   $223.3665   $223.37   $223.35   $223.40  
  Purchase #3 $181.41   5.162%   $190.7744   $190.77   $190.75   $190.80  
  Purchase #4 $209.93   11.823%   $234.75   $234.75   $234.75   $234.80  
  Purchase #5 $115.26   5.208%   $121.2627   $121.26   $121.25   $121.30  
  Purchase #6 $150.48   8.777%   $163.6876   $163.69   $163.70   $163.70  
  Purchase #7 $220.93   5.324%   $232.6923   $232.69   $232.70   $232.70  
  7 purchase totals = $1,146.85       $1,227.3702   $1,227.37   $1,227.35   $1,227.50