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 $84.99   10.605%   $94.0032   $94.00   $94.00   $94.00  
  Purchase #2 $21.27   9.241%   $23.2356   $23.24   $23.25   $23.20  
  Purchase #3 $147.97   9.195%   $161.5758   $161.58   $161.60   $161.60  
  Purchase #4 $125.98   9.858%   $138.3991   $138.40   $138.40   $138.40  
  Purchase #5 $81.28   13.813%   $92.5072   $92.51   $92.50   $92.50  
  Purchase #6 $240.85   11.387%   $268.2756   $268.28   $268.30   $268.30  
  Purchase #7 $152.42   12.783%   $171.9038   $171.90   $171.90   $171.90  
  7 purchase totals = $854.76       $949.9003   $949.91   $949.95   $949.90