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 $34.70   8.673%   $37.7095   $37.71   $37.70   $37.70  
  Purchase #2 $140.26   9.257%   $153.2439   $153.24   $153.25   $153.20  
  Purchase #3 $156.84   10.158%   $172.7718   $172.77   $172.75   $172.80  
  Purchase #4 $98.88   7.567%   $106.3622   $106.36   $106.35   $106.40  
  Purchase #5 $217.89   9.585%   $238.7748   $238.77   $238.75   $238.80  
  Purchase #6 $199.25   8.661%   $216.507   $216.51   $216.50   $216.50  
  Purchase #7 $111.80   5.373%   $117.807   $117.81   $117.80   $117.80  
  7 purchase totals = $959.62       $1,043.1762   $1,043.17   $1,043.10   $1,043.20