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 $81.25   5.823%   $85.9812   $85.98   $86.00   $86.00  
  Purchase #2 $92.35   9.382%   $101.0143   $101.01   $101.00   $101.00  
  Purchase #3 $227.70   10.527%   $251.67   $251.67   $251.65   $251.70  
  Purchase #4 $206.61   13.768%   $235.0561   $235.06   $235.05   $235.10  
  Purchase #5 $160.83   5.823%   $170.1951   $170.20   $170.20   $170.20  
  Purchase #6 $68.73   4.460%   $71.7954   $71.80   $71.80   $71.80  
  Purchase #7 $132.26   8.768%   $143.8566   $143.86   $143.85   $143.90  
  7 purchase totals = $969.73       $1,059.5687   $1,059.58   $1,059.55   $1,059.70