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 $192.32   8.859%   $209.3576   $209.36   $209.35   $209.40  
  Purchase #2 $157.95   12.395%   $177.5279   $177.53   $177.55   $177.50  
  Purchase #3 $72.36   13.227%   $81.9311   $81.93   $81.95   $81.90  
  Purchase #4 $153.94   11.246%   $171.2521   $171.25   $171.25   $171.30  
  Purchase #5 $191.61   9.349%   $209.5236   $209.52   $209.50   $209.50  
  Purchase #6 $154.75   3.160%   $159.6401   $159.64   $159.65   $159.60  
  Purchase #7 $138.97   8.668%   $151.0159   $151.02   $151.00   $151.00  
  7 purchase totals = $1,061.90       $1,160.2483   $1,160.25   $1,160.25   $1,160.20