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 $43.77   13.545%   $49.6986   $49.70   $49.70   $49.70  
  Purchase #2 $150.65   10.214%   $166.0374   $166.04   $166.05   $166.00  
  Purchase #3 $99.50   7.123%   $106.5874   $106.59   $106.60   $106.60  
  Purchase #4 $247.93   6.563%   $264.2016   $264.20   $264.20   $264.20  
  Purchase #5 $239.82   9.740%   $263.1785   $263.18   $263.20   $263.20  
  Purchase #6 $105.90   8.596%   $115.0032   $115.00   $115.00   $115.00  
  Purchase #7 $77.53   11.131%   $86.1599   $86.16   $86.15   $86.20  
  7 purchase totals = $965.10       $1,050.8666   $1,050.87   $1,050.90   $1,050.90