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 $58.38   12.184%   $65.493   $65.49   $65.50   $65.50  
  Purchase #2 $125.26   7.373%   $134.4954   $134.50   $134.50   $134.50  
  Purchase #3 $145.64   11.605%   $162.5415   $162.54   $162.55   $162.50  
  Purchase #4 $187.37   13.803%   $213.2327   $213.23   $213.25   $213.20  
  Purchase #5 $90.44   8.729%   $98.3345   $98.33   $98.35   $98.30  
  Purchase #6 $204.70   11.722%   $228.6949   $228.69   $228.70   $228.70  
  Purchase #7 $141.68   4.577%   $148.1647   $148.16   $148.15   $148.20  
  7 purchase totals = $953.47       $1,050.9567   $1,050.94   $1,051.00   $1,050.90