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 $116.92   6.353%   $124.3479   $124.35   $124.35   $124.30  
  Purchase #2 $164.46   6.773%   $175.5989   $175.60   $175.60   $175.60  
  Purchase #3 $242.98   9.480%   $266.0145   $266.01   $266.00   $266.00  
  Purchase #4 $98.86   13.556%   $112.2615   $112.26   $112.25   $112.30  
  Purchase #5 $190.52   4.392%   $198.8876   $198.89   $198.90   $198.90  
  Purchase #6 $188.59   3.234%   $194.689   $194.69   $194.70   $194.70  
  Purchase #7 $57.55   9.813%   $63.1974   $63.20   $63.20   $63.20  
  7 purchase totals = $1,059.88       $1,134.9968   $1,135.00   $1,135.00   $1,135.00