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 $213.60   10.459%   $235.9404   $235.94   $235.95   $235.90  
  Purchase #2 $160.48   3.834%   $166.6328   $166.63   $166.65   $166.60  
  Purchase #3 $192.42   4.166%   $200.4362   $200.44   $200.45   $200.40  
  Purchase #4 $36.86   9.473%   $40.3517   $40.35   $40.35   $40.40  
  Purchase #5 $241.33   9.813%   $265.0117   $265.01   $265.00   $265.00  
  Purchase #6 $112.83   8.810%   $122.7703   $122.77   $122.75   $122.80  
  Purchase #7 $155.41   3.326%   $160.5789   $160.58   $160.60   $160.60  
  7 purchase totals = $1,112.93       $1,191.7220   $1,191.72   $1,191.75   $1,191.70