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 $201.42   13.431%   $228.4727   $228.47   $228.45   $228.50  
  Purchase #2 $55.95   7.226%   $59.9929   $59.99   $60.00   $60.00  
  Purchase #3 $155.99   6.140%   $165.5678   $165.57   $165.55   $165.60  
  Purchase #4 $23.76   11.852%   $26.576   $26.58   $26.60   $26.60  
  Purchase #5 $31.95   11.107%   $35.4987   $35.50   $35.50   $35.50  
  Purchase #6 $92.86   3.764%   $96.3553   $96.36   $96.35   $96.40  
  Purchase #7 $248.90   4.384%   $259.8118   $259.81   $259.80   $259.80  
  7 purchase totals = $810.83       $872.2752   $872.28   $872.25   $872.40