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 $179.41   8.461%   $194.5899   $194.59   $194.60   $194.60  
  Purchase #2 $228.42   7.687%   $245.9786   $245.98   $246.00   $246.00  
  Purchase #3 $206.70   13.392%   $234.3813   $234.38   $234.40   $234.40  
  Purchase #4 $180.27   6.820%   $192.5644   $192.56   $192.55   $192.60  
  Purchase #5 $242.29   10.270%   $267.1732   $267.17   $267.15   $267.20  
  Purchase #6 $164.87   7.785%   $177.7051   $177.71   $177.70   $177.70  
  Purchase #7 $46.74   5.478%   $49.3004   $49.30   $49.30   $49.30  
  7 purchase totals = $1,248.70       $1,361.6929   $1,361.69   $1,361.70   $1,361.80