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 $65.27   4.714%   $68.3468   $68.35   $68.35   $68.30  
  Purchase #2 $178.96   13.249%   $202.6704   $202.67   $202.65   $202.70  
  Purchase #3 $98.38   11.182%   $109.3809   $109.38   $109.40   $109.40  
  Purchase #4 $165.54   3.424%   $171.2081   $171.21   $171.20   $171.20  
  Purchase #5 $176.35   8.822%   $191.9076   $191.91   $191.90   $191.90  
  Purchase #6 $194.86   3.805%   $202.2744   $202.27   $202.25   $202.30  
  Purchase #7 $11.74   6.775%   $12.5354   $12.54   $12.55   $12.50  
  7 purchase totals = $891.10       $958.3236   $958.33   $958.30   $958.30