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 $215.72   11.513%   $240.5558   $240.56   $240.55   $240.60  
  Purchase #2 $50.67   11.649%   $56.5725   $56.57   $56.55   $56.60  
  Purchase #3 $33.51   3.857%   $34.8025   $34.80   $34.80   $34.80  
  Purchase #4 $27.84   6.244%   $29.5783   $29.58   $29.60   $29.60  
  Purchase #5 $243.28   12.681%   $274.1303   $274.13   $274.15   $274.10  
  Purchase #6 $224.44   10.488%   $247.9793   $247.98   $248.00   $248.00  
  Purchase #7 $164.81   6.714%   $175.8753   $175.88   $175.90   $175.90  
  7 purchase totals = $960.27       $1,059.4940   $1,059.50   $1,059.55   $1,059.60