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 $171.30   12.777%   $193.187   $193.19   $193.20   $193.20  
  Purchase #2 $230.29   5.670%   $243.3474   $243.35   $243.35   $243.30  
  Purchase #3 $168.69   9.459%   $184.6464   $184.65   $184.65   $184.60  
  Purchase #4 $58.84   5.169%   $61.8814   $61.88   $61.90   $61.90  
  Purchase #5 $223.41   10.138%   $246.0593   $246.06   $246.05   $246.10  
  Purchase #6 $86.81   13.642%   $98.6526   $98.65   $98.65   $98.70  
  Purchase #7 $231.60   7.442%   $248.8357   $248.84   $248.85   $248.80  
  7 purchase totals = $1,170.94       $1,276.6098   $1,276.62   $1,276.65   $1,276.60