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 $92.39   5.282%   $97.27   $97.27   $97.25   $97.30  
  Purchase #2 $40.27   9.346%   $44.0336   $44.03   $44.05   $44.00  
  Purchase #3 $48.89   11.262%   $54.396   $54.40   $54.40   $54.40  
  Purchase #4 $101.54   8.658%   $110.3313   $110.33   $110.35   $110.30  
  Purchase #5 $246.77   6.752%   $263.4319   $263.43   $263.45   $263.40  
  Purchase #6 $179.68   3.395%   $185.7801   $185.78   $185.80   $185.80  
  Purchase #7 $236.52   5.203%   $248.8261   $248.83   $248.85   $248.80  
  7 purchase totals = $946.06       $1,004.0690   $1,004.07   $1,004.15   $1,004.00