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 $235.79   8.683%   $256.2636   $256.26   $256.25   $256.30  
  Purchase #2 $208.54   8.754%   $226.7956   $226.80   $226.80   $226.80  
  Purchase #3 $21.67   9.743%   $23.7813   $23.78   $23.80   $23.80  
  Purchase #4 $30.99   7.224%   $33.2287   $33.23   $33.25   $33.20  
  Purchase #5 $73.58   8.747%   $80.016   $80.02   $80.00   $80.00  
  Purchase #6 $218.28   12.630%   $245.8488   $245.85   $245.85   $245.80  
  Purchase #7 $184.91   5.441%   $194.971   $194.97   $194.95   $195.00  
  7 purchase totals = $973.76       $1,060.9050   $1,060.91   $1,060.90   $1,060.90