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 $118.66   11.274%   $132.0377   $132.04   $132.05   $132.00  
  Purchase #2 $174.64   8.715%   $189.8599   $189.86   $189.85   $189.90  
  Purchase #3 $27.73   3.675%   $28.7491   $28.75   $28.75   $28.70  
  Purchase #4 $93.35   3.537%   $96.6518   $96.65   $96.65   $96.70  
  Purchase #5 $184.26   10.166%   $202.9919   $202.99   $203.00   $203.00  
  Purchase #6 $142.48   5.609%   $150.4717   $150.47   $150.45   $150.50  
  Purchase #7 $175.67   5.592%   $185.4935   $185.49   $185.50   $185.50  
  7 purchase totals = $916.79       $986.2556   $986.25   $986.25   $986.30