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 $169.43   10.299%   $186.8796   $186.88   $186.90   $186.90  
  Purchase #2 $249.34   12.178%   $279.7046   $279.70   $279.70   $279.70  
  Purchase #3 $10.88   5.459%   $11.4739   $11.47   $11.45   $11.50  
  Purchase #4 $241.47   13.280%   $273.5372   $273.54   $273.55   $273.50  
  Purchase #5 $78.81   7.625%   $84.8193   $84.82   $84.80   $84.80  
  Purchase #6 $54.76   10.482%   $60.4999   $60.50   $60.50   $60.50  
  Purchase #7 $47.60   9.470%   $52.1077   $52.11   $52.10   $52.10  
  7 purchase totals = $852.29       $949.0222   $949.02   $949.00   $949.00