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 $163.84   8.555%   $177.8565   $177.86   $177.85   $177.90  
  Purchase #2 $116.63   7.329%   $125.1778   $125.18   $125.20   $125.20  
  Purchase #3 $75.90   7.747%   $81.78   $81.78   $81.80   $81.80  
  Purchase #4 $211.80   6.419%   $225.3954   $225.40   $225.40   $225.40  
  Purchase #5 $218.72   12.739%   $246.5827   $246.58   $246.60   $246.60  
  Purchase #6 $89.46   3.602%   $92.6823   $92.68   $92.70   $92.70  
  Purchase #7 $71.88   7.202%   $77.0568   $77.06   $77.05   $77.10  
  7 purchase totals = $948.23       $1,026.5315   $1,026.54   $1,026.60   $1,026.70