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 $216.95   8.813%   $236.0698   $236.07   $236.05   $236.10  
  Purchase #2 $87.81   9.422%   $96.0835   $96.08   $96.10   $96.10  
  Purchase #3 $204.89   12.406%   $230.3087   $230.31   $230.30   $230.30  
  Purchase #4 $60.54   12.417%   $68.0573   $68.06   $68.05   $68.10  
  Purchase #5 $216.44   3.743%   $224.5413   $224.54   $224.55   $224.50  
  Purchase #6 $62.35   11.593%   $69.5782   $69.58   $69.60   $69.60  
  Purchase #7 $87.64   13.229%   $99.2339   $99.23   $99.25   $99.20  
  7 purchase totals = $936.62       $1,023.8727   $1,023.87   $1,023.90   $1,023.90