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 $192.65   5.506%   $203.2573   $203.26   $203.25   $203.30  
  Purchase #2 $63.77   5.739%   $67.4298   $67.43   $67.45   $67.40  
  Purchase #3 $157.48   4.743%   $164.9493   $164.95   $164.95   $164.90  
  Purchase #4 $236.73   7.437%   $254.3356   $254.34   $254.35   $254.30  
  Purchase #5 $68.80   5.141%   $72.337   $72.34   $72.35   $72.30  
  Purchase #6 $172.55   9.760%   $189.3909   $189.39   $189.40   $189.40  
  Purchase #7 $242.97   6.493%   $258.746   $258.75   $258.75   $258.70  
  7 purchase totals = $1,134.95       $1,210.4459   $1,210.46   $1,210.50   $1,210.30