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 $76.54   8.734%   $83.225   $83.23   $83.25   $83.20  
  Purchase #2 $246.93   7.415%   $265.2399   $265.24   $265.25   $265.20  
  Purchase #3 $107.78   11.814%   $120.5131   $120.51   $120.50   $120.50  
  Purchase #4 $216.28   3.449%   $223.7395   $223.74   $223.75   $223.70  
  Purchase #5 $33.82   4.662%   $35.3967   $35.40   $35.40   $35.40  
  Purchase #6 $56.81   8.540%   $61.6616   $61.66   $61.65   $61.70  
  Purchase #7 $239.44   6.270%   $254.4529   $254.45   $254.45   $254.50  
  7 purchase totals = $977.60       $1,044.2287   $1,044.23   $1,044.25   $1,044.20