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 $164.85   11.731%   $184.1886   $184.19   $184.20   $184.20  
  Purchase #2 $122.53   6.841%   $130.9123   $130.91   $130.90   $130.90  
  Purchase #3 $149.34   5.469%   $157.5074   $157.51   $157.50   $157.50  
  Purchase #4 $55.53   8.468%   $60.2323   $60.23   $60.25   $60.20  
  Purchase #5 $193.91   10.121%   $213.5356   $213.54   $213.55   $213.50  
  Purchase #6 $126.86   12.229%   $142.3737   $142.37   $142.35   $142.40  
  Purchase #7 $210.39   9.374%   $230.112   $230.11   $230.10   $230.10  
  7 purchase totals = $1,023.41       $1,118.8619   $1,118.86   $1,118.85   $1,118.80