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 $142.92   10.761%   $158.2996   $158.30   $158.30   $158.30  
  Purchase #2 $208.26   13.779%   $236.9561   $236.96   $236.95   $237.00  
  Purchase #3 $160.65   7.539%   $172.7614   $172.76   $172.75   $172.80  
  Purchase #4 $118.40   6.490%   $126.0842   $126.08   $126.10   $126.10  
  Purchase #5 $90.55   13.711%   $102.9653   $102.97   $102.95   $103.00  
  Purchase #6 $191.73   4.295%   $199.9648   $199.96   $199.95   $200.00  
  Purchase #7 $200.28   3.243%   $206.7751   $206.78   $206.80   $206.80  
  7 purchase totals = $1,112.79       $1,203.8065   $1,203.81   $1,203.80   $1,204.00