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 $218.48   5.554%   $230.6144   $230.61   $230.60   $230.60  
  Purchase #2 $34.65   4.541%   $36.2235   $36.22   $36.20   $36.20  
  Purchase #3 $156.58   13.410%   $177.5774   $177.58   $177.60   $177.60  
  Purchase #4 $202.74   5.389%   $213.6657   $213.67   $213.65   $213.70  
  Purchase #5 $149.67   13.806%   $170.3334   $170.33   $170.35   $170.30  
  Purchase #6 $175.31   4.730%   $183.6022   $183.60   $183.60   $183.60  
  Purchase #7 $14.72   7.496%   $15.8234   $15.82   $15.80   $15.80  
  7 purchase totals = $952.15       $1,027.8400   $1,027.83   $1,027.80   $1,027.80