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 $218.76   10.585%   $241.9157   $241.92   $241.90   $241.90  
  Purchase #2 $165.77   6.639%   $176.7755   $176.78   $176.80   $176.80  
  Purchase #3 $61.70   7.137%   $66.1035   $66.10   $66.10   $66.10  
  Purchase #4 $152.78   13.367%   $173.2021   $173.20   $173.20   $173.20  
  Purchase #5 $36.90   7.392%   $39.6276   $39.63   $39.65   $39.60  
  Purchase #6 $36.40   8.219%   $39.3917   $39.39   $39.40   $39.40  
  Purchase #7 $124.56   11.856%   $139.3278   $139.33   $139.35   $139.30  
  7 purchase totals = $796.87       $876.3439   $876.35   $876.40   $876.30