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 $104.31   5.104%   $109.634   $109.63   $109.65   $109.60  
  Purchase #2 $143.73   8.129%   $155.4138   $155.41   $155.40   $155.40  
  Purchase #3 $67.97   3.291%   $70.2069   $70.21   $70.20   $70.20  
  Purchase #4 $227.39   7.406%   $244.2305   $244.23   $244.25   $244.20  
  Purchase #5 $247.59   4.385%   $258.4468   $258.45   $258.45   $258.40  
  Purchase #6 $45.28   10.511%   $50.0394   $50.04   $50.05   $50.00  
  Purchase #7 $197.28   3.177%   $203.5476   $203.55   $203.55   $203.50  
  7 purchase totals = $1,033.55       $1,091.5190   $1,091.52   $1,091.55   $1,091.30