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 $119.42   6.712%   $127.4355   $127.44   $127.45   $127.40  
  Purchase #2 $55.27   9.555%   $60.551   $60.55   $60.55   $60.60  
  Purchase #3 $41.94   8.127%   $45.3485   $45.35   $45.35   $45.30  
  Purchase #4 $113.28   5.349%   $119.3393   $119.34   $119.35   $119.30  
  Purchase #5 $9.96   9.775%   $10.9336   $10.93   $10.95   $10.90  
  Purchase #6 $242.59   11.646%   $270.842   $270.84   $270.85   $270.80  
  Purchase #7 $145.68   11.786%   $162.8498   $162.85   $162.85   $162.80  
  7 purchase totals = $728.14       $797.2997   $797.30   $797.35   $797.10