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 $91.89   11.697%   $102.6384   $102.64   $102.65   $102.60  
  Purchase #2 $234.67   8.579%   $254.8023   $254.80   $254.80   $254.80  
  Purchase #3 $151.63   8.292%   $164.2032   $164.20   $164.20   $164.20  
  Purchase #4 $181.33   3.149%   $187.0401   $187.04   $187.05   $187.00  
  Purchase #5 $59.68   13.188%   $67.5506   $67.55   $67.55   $67.60  
  Purchase #6 $204.99   6.677%   $218.6772   $218.68   $218.70   $218.70  
  Purchase #7 $18.27   6.784%   $19.5094   $19.51   $19.50   $19.50  
  7 purchase totals = $942.46       $1,014.4212   $1,014.42   $1,014.45   $1,014.40