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 $48.81   13.287%   $55.2954   $55.30   $55.30   $55.30  
  Purchase #2 $81.57   3.110%   $84.1068   $84.11   $84.10   $84.10  
  Purchase #3 $216.37   10.296%   $238.6475   $238.65   $238.65   $238.60  
  Purchase #4 $227.55   10.527%   $251.5042   $251.50   $251.50   $251.50  
  Purchase #5 $195.26   10.847%   $216.4399   $216.44   $216.45   $216.40  
  Purchase #6 $61.50   12.574%   $69.233   $69.23   $69.25   $69.20  
  Purchase #7 $42.41   7.821%   $45.7269   $45.73   $45.75   $45.70  
  7 purchase totals = $873.47       $960.9537   $960.96   $961.00   $960.80