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 $229.65   7.467%   $246.798   $246.80   $246.80   $246.80  
  Purchase #2 $52.66   11.471%   $58.7006   $58.70   $58.70   $58.70  
  Purchase #3 $218.69   11.221%   $243.2292   $243.23   $243.25   $243.20  
  Purchase #4 $97.70   6.220%   $103.7769   $103.78   $103.80   $103.80  
  Purchase #5 $41.78   11.715%   $46.6745   $46.67   $46.65   $46.70  
  Purchase #6 $90.55   4.436%   $94.5668   $94.57   $94.55   $94.60  
  Purchase #7 $120.73   8.436%   $130.9148   $130.91   $130.90   $130.90  
  7 purchase totals = $851.76       $924.6608   $924.66   $924.65   $924.70