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 $38.97   10.852%   $43.199   $43.20   $43.20   $43.20  
  Purchase #2 $111.88   7.203%   $119.9387   $119.94   $119.95   $119.90  
  Purchase #3 $204.93   4.745%   $214.6539   $214.65   $214.65   $214.70  
  Purchase #4 $249.51   3.874%   $259.176   $259.18   $259.20   $259.20  
  Purchase #5 $77.86   4.492%   $81.3575   $81.36   $81.35   $81.40  
  Purchase #6 $40.33   13.563%   $45.8   $45.80   $45.80   $45.80  
  Purchase #7 $166.37   11.102%   $184.8404   $184.84   $184.85   $184.80  
  7 purchase totals = $889.85       $948.9655   $948.97   $949.00   $949.00