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 $7.64   13.215%   $8.6496   $8.65   $8.65   $8.60  
  Purchase #2 $121.37   10.642%   $134.2862   $134.29   $134.30   $134.30  
  Purchase #3 $15.71   13.243%   $17.7905   $17.79   $17.80   $17.80  
  Purchase #4 $155.55   3.574%   $161.1094   $161.11   $161.10   $161.10  
  Purchase #5 $250.55   6.838%   $267.6826   $267.68   $267.70   $267.70  
  Purchase #6 $230.53   7.309%   $247.3794   $247.38   $247.40   $247.40  
  Purchase #7 $54.52   5.354%   $57.439   $57.44   $57.45   $57.40  
  7 purchase totals = $835.87       $894.3367   $894.34   $894.40   $894.30