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 $76.41   7.281%   $81.9734   $81.97   $81.95   $82.00  
  Purchase #2 $232.46   8.385%   $251.9518   $251.95   $251.95   $252.00  
  Purchase #3 $178.73   4.571%   $186.8997   $186.90   $186.90   $186.90  
  Purchase #4 $42.55   8.806%   $46.297   $46.30   $46.30   $46.30  
  Purchase #5 $232.97   4.313%   $243.018   $243.02   $243.00   $243.00  
  Purchase #6 $52.42   7.408%   $56.3033   $56.30   $56.30   $56.30  
  Purchase #7 $46.73   11.391%   $52.053   $52.05   $52.05   $52.10  
  7 purchase totals = $862.27       $918.4962   $918.49   $918.45   $918.60